diff --git a/MANIFEST.in b/MANIFEST.in
index 7451fb54375..c4086f8b731 100644
--- a/MANIFEST.in
+++ b/MANIFEST.in
@@ -1 +1,4 @@
 global-include ansys.aedt.core *.txt *.md *.toml *.json *.png *.xml *.areg *.joblib *.acf *.m *.ipynb *.py_build
+include src/ansys/aedt/core/syslib/**/*.so
+include src/ansys/aedt/core/syslib/**/*.pyd
+include src/ansys/aedt/core/syslib/**/*.license
\ No newline at end of file
diff --git a/doc/changelog.d/6236.miscellaneous.md b/doc/changelog.d/6236.miscellaneous.md
new file mode 100644
index 00000000000..09b6a2a7bee
--- /dev/null
+++ b/doc/changelog.d/6236.miscellaneous.md
@@ -0,0 +1 @@
+Nastran import refactoring
\ No newline at end of file
diff --git a/pyproject.toml b/pyproject.toml
index 1646c9aa799..3f9256b616d 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -131,6 +131,12 @@ examples = [
     "scikit-rf>=0.30.0,<1.8",
 ]
 
+[tool.setuptools]
+include-package-data = true
+
+[tool.setuptools.package-data]
+"ansys.aedt.core.syslib" = ["**/*.so", "**/*.pyd", "**/*.license"]
+
 [tool.setuptools.dynamic]
 version = {attr = "ansys.aedt.core.__version__"}
 
diff --git a/src/ansys/aedt/core/extensions/project/import_nastran.py b/src/ansys/aedt/core/extensions/project/import_nastran.py
index fc61ea24614..768ac0b6911 100644
--- a/src/ansys/aedt/core/extensions/project/import_nastran.py
+++ b/src/ansys/aedt/core/extensions/project/import_nastran.py
@@ -36,7 +36,7 @@
 from ansys.aedt.core.extensions.misc import get_port
 from ansys.aedt.core.extensions.misc import get_process_id
 from ansys.aedt.core.extensions.misc import is_student
-from ansys.aedt.core.visualization.advanced.misc import nastran_to_stl
+from ansys.aedt.core.syslib.nastran_import import nastran_to_stl
 
 
 @dataclass
@@ -45,6 +45,7 @@ class ExtensionData:
     lightweight: bool = False
     planar: bool = True
     file_path: str = ""
+    remove_multiple_connections: bool = False
 
 
 PORT = get_port()
@@ -52,7 +53,13 @@ class ExtensionData:
 AEDT_PROCESS_ID = get_process_id()
 IS_STUDENT = is_student()
 EXTENSION_TITLE = "Import Nastran or STL file"
-EXTENSION_DEFAULT_ARGUMENTS = {"decimate": 0.0, "lightweight": False, "planar": True, "file_path": ""}
+EXTENSION_DEFAULT_ARGUMENTS = {
+    "decimate": 0.0,
+    "lightweight": False,
+    "planar": True,
+    "file_path": "",
+    "remove_multiple_connections": False,
+}
 
 result = None
 
@@ -78,6 +85,7 @@ def browseFiles():
             title="Select a Nastran or stl File",
             filetypes=(("Nastran", "*.nas"), ("STL", "*.stl"), ("all files", "*.*")),
         )
+        text.delete("1.0", tkinter.END)
         text.insert(tkinter.END, filename)
 
     b1 = ttk.Button(root, text="...", width=10, command=browseFiles, style="PyAEDT.TButton", name="browse_button")
@@ -103,6 +111,17 @@ def browseFiles():
     check3 = ttk.Checkbutton(root, variable=planar, style="PyAEDT.TCheckbutton", name="check_planar_merge")
     check3.grid(row=3, column=1, pady=10, padx=5)
 
+    label = ttk.Label(root, text="Remove multiple connections:", style="PyAEDT.TLabel")
+    label.grid(row=4, column=0, pady=10)
+    remove_multiple_connections = tkinter.IntVar(root, value=0)
+    check4 = ttk.Checkbutton(
+        root,
+        variable=remove_multiple_connections,
+        style="PyAEDT.TCheckbutton",
+        name="check_remove_multiple_connections",
+    )
+    check4.grid(row=4, column=1, pady=10, padx=5)
+
     def toggle_theme():
         if root.theme == "light":
             set_dark_theme()
@@ -145,6 +164,7 @@ def callback():
             lightweight=True if light.get() == 1 else False,
             planar=True if planar.get() == 1 else False,
             file_path=text.get("1.0", tkinter.END).strip(),
+            remove_multiple_connections=True if remove_multiple_connections.get() == 1 else False,
         )
         root.destroy()
 
@@ -160,9 +180,9 @@ def preview():
         if file_path_ui.endswith(".nas"):
             nastran_to_stl(file_path_ui, decimation=decimate_ui, preview=True)
         else:
-            from ansys.aedt.core.visualization.advanced.misc import simplify_stl
+            from ansys.aedt.core.visualization.advanced.misc import simplify_and_preview_stl
 
-            simplify_stl(file_path_ui, decimation=decimate_ui, preview=True)
+            simplify_and_preview_stl(file_path_ui, decimation=decimate_ui, preview=True)
 
     b2 = ttk.Button(root, text="Preview", width=40, command=preview, style="PyAEDT.TButton", name="preview_button")
     b2.grid(row=5, column=0, pady=10, padx=10)
@@ -178,6 +198,7 @@ def main(extension_args):
     lightweight = extension_args["lightweight"]
     decimate = extension_args["decimate"]
     planar = extension_args["planar"]
+    remove_multiple_connections = extension_args["remove_multiple_connections"]
 
     if file_path.is_file():
         app = ansys.aedt.core.Desktop(
@@ -198,12 +219,16 @@ def main(extension_args):
 
         if file_path.suffix == ".nas":
             aedtapp.modeler.import_nastran(
-                str(file_path), import_as_light_weight=lightweight, decimation=decimate, enable_planar_merge=str(planar)
+                str(file_path),
+                import_as_light_weight=lightweight,
+                decimation=decimate,
+                enable_planar_merge=str(planar),
+                remove_multiple_connections=remove_multiple_connections,
             )
         else:
-            from ansys.aedt.core.visualization.advanced.misc import simplify_stl
+            from ansys.aedt.core.visualization.advanced.misc import simplify_and_preview_stl
 
-            outfile = simplify_stl(str(file_path), decimation=decimate)
+            outfile = simplify_and_preview_stl(str(file_path), decimation=decimate)
             aedtapp.modeler.import_3d_cad(
                 outfile, healing=False, create_lightweigth_part=lightweight, merge_planar_faces=planar
             )
diff --git a/src/ansys/aedt/core/generic/general_methods.py b/src/ansys/aedt/core/generic/general_methods.py
index dbe8eb36d6c..4a19c9649aa 100644
--- a/src/ansys/aedt/core/generic/general_methods.py
+++ b/src/ansys/aedt/core/generic/general_methods.py
@@ -31,6 +31,7 @@
 import itertools
 import logging
 import os
+import platform
 import re
 import sys
 import time
@@ -47,8 +48,11 @@
 from ansys.aedt.core.internal.errors import GrpcApiError
 from ansys.aedt.core.internal.errors import MethodNotSupportedError
 
-is_linux = os.name == "posix"
-is_windows = not is_linux
+system = platform.system()
+is_linux = system == "Linux"
+is_windows = system == "Windows"
+is_macos = system == "Darwin"
+
 inside_desktop = True if "4.0.30319.42000" in sys.version else False
 
 inclusion_list = [
diff --git a/src/ansys/aedt/core/generic/settings.py b/src/ansys/aedt/core/generic/settings.py
index 597ca3f3d20..a7b37f63943 100644
--- a/src/ansys/aedt/core/generic/settings.py
+++ b/src/ansys/aedt/core/generic/settings.py
@@ -38,6 +38,7 @@
 
 import logging
 import os
+from pathlib import Path
 import time
 from typing import Any
 from typing import List
@@ -45,6 +46,8 @@
 from typing import Union
 import uuid
 
+from ansys.aedt.core import pyaedt_path
+
 is_linux = os.name == "posix"
 
 # Settings allowed to be updated using a YAML configuration file.
@@ -102,6 +105,8 @@
     "remote_rpc_session_temp_folder",
     "block_figure_plot",
     "skip_license_check",
+    "pyd_libraries_path",
+    "pyd_libraries_user_path",
 ]
 ALLOWED_AEDT_ENV_VAR_SETTINGS = [
     "ANSYSEM_FEATURE_F335896_MECHANICAL_STRUCTURAL_SOLN_TYPE_ENABLE",
@@ -172,7 +177,7 @@ def __init__(self):
         self.__lsf_queue: Optional[str] = None
         self.__custom_lsf_command: Optional[str] = None
         # Settings related to environment variables that are set before launching a new AEDT session
-        # This includes those that enable the beta features !
+        # This includes those that enable the beta features!
         self.__aedt_environment_variables: dict[str, str] = {
             "ANSYSEM_FEATURE_SF6694_NON_GRAPHICAL_COMMAND_EXECUTION_ENABLE": "1",
             "ANSYSEM_FEATURE_SF159726_SCRIPTOBJECT_ENABLE": "1",
@@ -214,6 +219,8 @@ def __init__(self):
         self.__time_tick = time.time()
         self.__pyaedt_server_path = ""
         self.__block_figure_plot = False
+        self.__pyd_libraries_path: Path = Path(pyaedt_path) / "syslib"
+        self.__pyd_libraries_user_path: Optional[str] = None
 
         # Load local settings if YAML configuration file exists.
         pyaedt_settings_path = os.environ.get("PYAEDT_LOCAL_SETTINGS_PATH", "")
@@ -785,6 +792,36 @@ def skip_license_check(self):
     def skip_license_check(self, value):
         self.__skip_license_check = value
 
+    @property
+    def pyd_libraries_path(self):
+        if self.__pyd_libraries_user_path is not None:
+            # If the user path is set, return it
+            return Path(self.__pyd_libraries_user_path)
+        return Path(self.__pyd_libraries_path)
+
+    @property
+    def pyd_libraries_user_path(self):
+        # Get the user path for PyAEDT libraries.
+        if self.__pyd_libraries_user_path is not None:
+            return Path(self.__pyd_libraries_user_path)
+        return None
+
+    @pyd_libraries_user_path.setter
+    def pyd_libraries_user_path(self, val):
+        if val is None:
+            # If the user path is None, set it to None
+            self.__pyd_libraries_user_path = None
+        else:
+            lib_path = Path(str(val))
+            if not lib_path.exists():
+                # If the user path does not exist, return None
+                raise ValueError("The user path for PyAEDT libraries does not exist. Please set a valid path.")
+            else:
+                # If the user path exists, set it as a Path object
+                self.__pyd_libraries_user_path = lib_path
+
+    # yaml setting file IO methods
+
     def load_yaml_configuration(self, path: str, raise_on_wrong_key: bool = False):
         """Update default settings from a YAML configuration file."""
         import yaml
@@ -825,15 +862,22 @@ def filter_settings_with_raise(settings: dict, allowed_keys: List[str]):
                     raise KeyError("An environment variable key is not part of the allowed keys.")
                 self.aedt_environment_variables = settings
 
-    def writte_yaml_configuration(self, path: str):
+    def write_yaml_configuration(self, path: str):
         """Write the current settings into a YAML configuration file."""
         import yaml
 
         data = {}
-        data["log"] = {key: getattr(self, key) for key in ALLOWED_LOG_SETTINGS}
-        data["lsf"] = {key: getattr(self, key) for key in ALLOWED_LSF_SETTINGS}
+        data["log"] = {
+            key: str(value) if isinstance(value := getattr(self, key), Path) else value for key in ALLOWED_LOG_SETTINGS
+        }
+        data["lsf"] = {
+            key: str(value) if isinstance(value := getattr(self, key), Path) else value for key in ALLOWED_LSF_SETTINGS
+        }
         data["aedt_env_var"] = getattr(self, "aedt_environment_variables")
-        data["general"] = {key: getattr(self, key) for key in ALLOWED_GENERAL_SETTINGS}
+        data["general"] = {
+            key: str(value) if isinstance(value := getattr(self, key), Path) else value
+            for key in ALLOWED_GENERAL_SETTINGS
+        }
 
         with open(path, "w") as file:
             yaml.safe_dump(data, file, sort_keys=False)
diff --git a/src/ansys/aedt/core/modeler/modeler_3d.py b/src/ansys/aedt/core/modeler/modeler_3d.py
index f68627cbd57..5e75260b6e0 100644
--- a/src/ansys/aedt/core/modeler/modeler_3d.py
+++ b/src/ansys/aedt/core/modeler/modeler_3d.py
@@ -36,7 +36,7 @@
 from ansys.aedt.core.internal.errors import GrpcApiError
 from ansys.aedt.core.modeler.cad.primitives_3d import Primitives3D
 from ansys.aedt.core.modeler.geometry_operators import GeometryOperators
-from ansys.aedt.core.visualization.advanced.misc import nastran_to_stl
+from ansys.aedt.core.syslib.nastran_import import nastran_to_stl
 
 
 class Modeler3D(Primitives3D):
@@ -1029,6 +1029,7 @@ def import_nastran(
         save_only_stl=False,
         preview=False,
         merge_angle=1e-3,
+        remove_multiple_connections=False,
     ):
         """Import Nastran file into 3D Modeler by converting the faces to stl and reading it.
 
@@ -1060,6 +1061,8 @@ def import_nastran(
             Whether to preview the model in pyvista or skip it.
         merge_angle : float, optional
             Angle in radians for which faces will be considered planar. Default is ``1e-3``.
+        remove_multiple_connections : bool, optional
+            Whether to remove multiple connections in the mesh. Default is ``False``.
 
         Returns
         -------
@@ -1078,6 +1081,7 @@ def import_nastran(
             output_folder=self._app.working_directory,
             enable_planar_merge=enable_planar_merge,
             preview=preview,
+            remove_multiple_connections=remove_multiple_connections,
         )
         if save_only_stl:
             return output_stls, nas_to_dict
diff --git a/src/ansys/aedt/core/syslib/__init__.py b/src/ansys/aedt/core/syslib/__init__.py
new file mode 100644
index 00000000000..df6761d7662
--- /dev/null
+++ b/src/ansys/aedt/core/syslib/__init__.py
@@ -0,0 +1,92 @@
+# -*- coding: utf-8 -*-
+#
+# Copyright (C) 2021 - 2025 ANSYS, Inc. and/or its affiliates.
+# SPDX-License-Identifier: MIT
+#
+#
+# Permission is hereby granted, free of charge, to any person obtaining a copy
+# of this software and associated documentation files (the "Software"), to deal
+# in the Software without restriction, including without limitation the rights
+# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+# copies of the Software, and to permit persons to whom the Software is
+# furnished to do so, subject to the following conditions:
+#
+# The above copyright notice and this permission notice shall be included in all
+# copies or substantial portions of the Software.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+# SOFTWARE.
+
+import importlib.util
+from pathlib import Path
+import sys
+
+from ansys.aedt.core.generic.general_methods import is_windows
+
+
+def load_native_module(module_name: str, base_dir: Path | str) -> object:
+    """
+    Dynamically load a compiled native Python module (.pyd or .so) from a base directory.
+    Automatically choose the correct file extension based on the platform and Python version.
+
+    The module name must end with '_lib' or '_dynload'.
+
+    Example:
+        module_name='nastran_import_lib' on Python 3.11 → loads 'nastran_import_lib_311.so' on Linux
+
+    Parameters
+    ----------
+        module_name: str
+            The name of the module to load (e.g. 'nastran_import').
+
+        base_dir: Path, str
+            Path to the directory containing the compiled module.
+
+    Returns
+    -------
+        The loaded module object.
+
+    Raises
+    ------
+        FileNotFoundError: If the compiled module file is not found.
+        ImportError: If the module cannot be imported.
+    """
+    base_path = Path(base_dir)
+
+    # Validate the module name
+    if not module_name.endswith(("_lib", "_dynload")):
+        raise ValueError("Module name must end with '_lib' or '_dynload'.")
+
+    # Get Python version as suffix (e.g., '311' for Python 3.11)
+    version_suffix = f"{sys.version_info.major}{sys.version_info.minor}"
+
+    if version_suffix not in ["310", "311", "312", "313"]:
+        raise ValueError(
+            f"Unsupported Python version for {module_name}: {sys.version_info.major}.{sys.version_info.minor} \n"
+            f"Supported versions are 3.10, 3.11, 3.12, and 3.13."
+        )
+
+    # Determine the platform-specific extension
+    ext = ".pyd" if is_windows else ".so"
+
+    # Construct the full module path
+    file_name = f"{module_name}_{version_suffix}{ext}"
+    module_path = base_path / file_name
+
+    if not module_path.is_file():
+        raise FileNotFoundError(f"Module file not found at: {module_path}")
+
+    spec = importlib.util.spec_from_file_location(module_name, str(module_path))
+    if spec is None or spec.loader is None:
+        raise ImportError(f"Failed to create import spec for {module_path}")
+
+    mod = importlib.util.module_from_spec(spec)
+    sys.modules[module_name] = mod
+    spec.loader.exec_module(mod)
+
+    return mod
diff --git a/src/ansys/aedt/core/syslib/nastran_import/__init__.py b/src/ansys/aedt/core/syslib/nastran_import/__init__.py
new file mode 100644
index 00000000000..8b760ced1bb
--- /dev/null
+++ b/src/ansys/aedt/core/syslib/nastran_import/__init__.py
@@ -0,0 +1,74 @@
+# -*- coding: utf-8 -*-
+#
+# Copyright (C) 2021 - 2025 ANSYS, Inc. and/or its affiliates.
+# SPDX-License-Identifier: MIT
+#
+#
+# Permission is hereby granted, free of charge, to any person obtaining a copy
+# of this software and associated documentation files (the "Software"), to deal
+# in the Software without restriction, including without limitation the rights
+# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+# copies of the Software, and to permit persons to whom the Software is
+# furnished to do so, subject to the following conditions:
+#
+# The above copyright notice and this permission notice shall be included in all
+# copies or substantial portions of the Software.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+# SOFTWARE.
+
+from ansys.aedt.core.generic.file_utils import open_file
+from ansys.aedt.core.generic.general_methods import pyaedt_function_handler
+from ansys.aedt.core.generic.settings import settings
+from ansys.aedt.core.modeler.geometry_operators import GeometryOperators
+from ansys.aedt.core.syslib import load_native_module
+from ansys.aedt.core.visualization.advanced.misc import preview_pyvista
+
+__all__ = ["nastran_to_stl"]
+
+# Dynamically load the compiled nastran_import module from a directory
+_nastran_import_lib = load_native_module("nastran_import_lib", settings.pyd_libraries_path / "nastran_import")
+
+# Initialize the helpers for the nastran_import_lib module
+_nastran_import_lib.initialize_helpers(open_file, GeometryOperators, preview_pyvista)
+
+
+@pyaedt_function_handler()
+def nastran_to_stl(*args, **kwargs):
+    """Convert a Nastran file to STL format.
+
+    Parameters
+    ----------
+    input_file : str
+        Path to the input Nastran file.
+    output_folder : str, optional
+        Path to the output folder where the STL files will be saved.
+        If ``None``, the directory of the input file is used.
+    decimation : int, optional
+        The decimation factor for mesh simplification.
+        Default is ``0`` (no decimation).
+    enable_planar_merge : str, optional
+        Whether to enable or not planar merge. It can be ``"True"``, ``"False"`` or ``"Auto"``.
+        ``"Auto"`` will disable the planar merge if stl contains more than 50000 triangles.
+    preview : bool, optional
+        Whether to generate a preview of the STL files using PyVista.
+        Default is ``False``.
+    remove_multiple_connections : bool, optional
+        Whether to remove multiple connections in the mesh.
+        Default is ``False``.
+
+    Returns
+    -------
+    tuple
+        A tuple containing:
+            - A list of paths to the generated STL files.
+            - A dictionary representing the parsed Nastran data.
+            - A boolean indicating whether planar merging was enabled.
+
+    """
+    return _nastran_import_lib.nastran_to_stl(*args, **kwargs)
diff --git a/src/ansys/aedt/core/syslib/nastran_import/nastran_import_lib_310.pyd b/src/ansys/aedt/core/syslib/nastran_import/nastran_import_lib_310.pyd
new file mode 100644
index 00000000000..8f8be6d6c08
Binary files /dev/null and b/src/ansys/aedt/core/syslib/nastran_import/nastran_import_lib_310.pyd differ
diff --git a/src/ansys/aedt/core/syslib/nastran_import/nastran_import_lib_310.pyd.license b/src/ansys/aedt/core/syslib/nastran_import/nastran_import_lib_310.pyd.license
new file mode 100644
index 00000000000..e9617127c93
--- /dev/null
+++ b/src/ansys/aedt/core/syslib/nastran_import/nastran_import_lib_310.pyd.license
@@ -0,0 +1,23 @@
+-*- coding: utf-8 -*-
+
+Copyright (C) 2021 - 2025 ANSYS, Inc. and/or its affiliates.
+SPDX-License-Identifier: MIT
+
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
diff --git a/src/ansys/aedt/core/syslib/nastran_import/nastran_import_lib_310.so b/src/ansys/aedt/core/syslib/nastran_import/nastran_import_lib_310.so
new file mode 100644
index 00000000000..e63ad839970
Binary files /dev/null and b/src/ansys/aedt/core/syslib/nastran_import/nastran_import_lib_310.so differ
diff --git a/src/ansys/aedt/core/syslib/nastran_import/nastran_import_lib_311.pyd b/src/ansys/aedt/core/syslib/nastran_import/nastran_import_lib_311.pyd
new file mode 100644
index 00000000000..2ea07656e66
Binary files /dev/null and b/src/ansys/aedt/core/syslib/nastran_import/nastran_import_lib_311.pyd differ
diff --git a/src/ansys/aedt/core/syslib/nastran_import/nastran_import_lib_311.pyd.license b/src/ansys/aedt/core/syslib/nastran_import/nastran_import_lib_311.pyd.license
new file mode 100644
index 00000000000..e9617127c93
--- /dev/null
+++ b/src/ansys/aedt/core/syslib/nastran_import/nastran_import_lib_311.pyd.license
@@ -0,0 +1,23 @@
+-*- coding: utf-8 -*-
+
+Copyright (C) 2021 - 2025 ANSYS, Inc. and/or its affiliates.
+SPDX-License-Identifier: MIT
+
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
diff --git a/src/ansys/aedt/core/syslib/nastran_import/nastran_import_lib_311.so b/src/ansys/aedt/core/syslib/nastran_import/nastran_import_lib_311.so
new file mode 100644
index 00000000000..54526d9478b
Binary files /dev/null and b/src/ansys/aedt/core/syslib/nastran_import/nastran_import_lib_311.so differ
diff --git a/src/ansys/aedt/core/syslib/nastran_import/nastran_import_lib_312.pyd b/src/ansys/aedt/core/syslib/nastran_import/nastran_import_lib_312.pyd
new file mode 100644
index 00000000000..64e59798cb6
Binary files /dev/null and b/src/ansys/aedt/core/syslib/nastran_import/nastran_import_lib_312.pyd differ
diff --git a/src/ansys/aedt/core/syslib/nastran_import/nastran_import_lib_312.pyd.license b/src/ansys/aedt/core/syslib/nastran_import/nastran_import_lib_312.pyd.license
new file mode 100644
index 00000000000..e9617127c93
--- /dev/null
+++ b/src/ansys/aedt/core/syslib/nastran_import/nastran_import_lib_312.pyd.license
@@ -0,0 +1,23 @@
+-*- coding: utf-8 -*-
+
+Copyright (C) 2021 - 2025 ANSYS, Inc. and/or its affiliates.
+SPDX-License-Identifier: MIT
+
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
diff --git a/src/ansys/aedt/core/syslib/nastran_import/nastran_import_lib_312.so b/src/ansys/aedt/core/syslib/nastran_import/nastran_import_lib_312.so
new file mode 100644
index 00000000000..c27657568c4
Binary files /dev/null and b/src/ansys/aedt/core/syslib/nastran_import/nastran_import_lib_312.so differ
diff --git a/src/ansys/aedt/core/syslib/nastran_import/nastran_import_lib_313.pyd b/src/ansys/aedt/core/syslib/nastran_import/nastran_import_lib_313.pyd
new file mode 100644
index 00000000000..f567003b24c
Binary files /dev/null and b/src/ansys/aedt/core/syslib/nastran_import/nastran_import_lib_313.pyd differ
diff --git a/src/ansys/aedt/core/syslib/nastran_import/nastran_import_lib_313.pyd.license b/src/ansys/aedt/core/syslib/nastran_import/nastran_import_lib_313.pyd.license
new file mode 100644
index 00000000000..e9617127c93
--- /dev/null
+++ b/src/ansys/aedt/core/syslib/nastran_import/nastran_import_lib_313.pyd.license
@@ -0,0 +1,23 @@
+-*- coding: utf-8 -*-
+
+Copyright (C) 2021 - 2025 ANSYS, Inc. and/or its affiliates.
+SPDX-License-Identifier: MIT
+
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
diff --git a/src/ansys/aedt/core/syslib/nastran_import/nastran_import_lib_313.so b/src/ansys/aedt/core/syslib/nastran_import/nastran_import_lib_313.so
new file mode 100644
index 00000000000..4a87f359df7
Binary files /dev/null and b/src/ansys/aedt/core/syslib/nastran_import/nastran_import_lib_313.so differ
diff --git a/src/ansys/aedt/core/visualization/advanced/misc.py b/src/ansys/aedt/core/visualization/advanced/misc.py
index 9d535f8564a..702a33c11ff 100644
--- a/src/ansys/aedt/core/visualization/advanced/misc.py
+++ b/src/ansys/aedt/core/visualization/advanced/misc.py
@@ -279,451 +279,81 @@ def parse_rdat_file(file_path):
     return report_dict
 
 
-@pyaedt_function_handler()
-def _parse_nastran(file_path):
-    """Nastran file parser."""
-
-    if not Path(file_path).exists():
-        raise FileNotFoundError(f"File ({file_path}) not found")
-
-    logger = logging.getLogger("Global")
-    nas_to_dict = {"Points": [], "PointsId": {}, "Assemblies": {}}
-    includes = []
-
-    def parse_lines(input_lines, input_pid=0, in_assembly="Main"):
-        if in_assembly not in nas_to_dict["Assemblies"]:
-            nas_to_dict["Assemblies"][in_assembly] = {"Triangles": {}, "Solids": {}, "Lines": {}, "Shells": {}}
-
-        def get_point(ll, start, length):
-            n = ll[start : start + length].strip()
-            if "-" in n[1:] and "e" not in n[1:].lower():
-                n = n[0] + n[1:].replace("-", "e-")
-            return n
-
-        line_header = ""
-        for lk in range(len(input_lines)):
-            line = input_lines[lk]
-            line_type = line[:8].strip()
-            obj_type = "Triangles"
-            if line.startswith("$"):
-                line_header = line[1:]
-                continue
-            elif line.startswith("*"):
-                continue
-            elif line_type in ["GRID", "GRID*"]:
-                num_points = 3
-                obj_type = "Grid"
-            elif line_type in [
-                "CTRIA3",
-                "CTRIA3*",
-            ]:
-                num_points = 3
-                obj_type = "Triangles"
-            elif line_type in ["CROD", "CBEAM", "CBAR", "CROD*", "CBEAM*", "CBAR*"]:
-                num_points = 2
-                obj_type = "Lines"
-            elif line_type in [
-                "CQUAD4",
-                "CQUAD4*",
-            ]:
-                num_points = 4
-                obj_type = "Triangles"
-            elif line_type in ["CTETRA", "CTETRA*"]:
-                num_points = 4
-                obj_type = "Solids"
-            elif line_type in ["CPYRA", "CPYRAM", "CPYRA*", "CPYRAM*"]:
-                num_points = 5
-                obj_type = "Solids"
-            elif line_type in ["CHEXA", "CHEXA*"]:
-                num_points = 8
-                obj_type = "Solids"
-            elif line_type in ["PSHELL", "PSHELL*"]:
-                num_points = 1
-                obj_type = "Shells"
-            elif line_type in ["MPC", "MPC*"]:
-                num_points = 16
-            else:
-                continue
-
-            points = []
-            start_pointer = 8
-            word_length = 8
-            if line_type.endswith("*"):
-                word_length = 16
-            grid_id = int(line[start_pointer : start_pointer + word_length])
-            pp = 0
-            start_pointer = start_pointer + word_length
-            object_id = line[start_pointer : start_pointer + word_length]
-            if obj_type == "Shells":
-                nas_to_dict["Assemblies"][in_assembly][obj_type][grid_id] = []
-            elif obj_type != "Grid":
-                object_id = int(object_id)
-                if object_id not in nas_to_dict["Assemblies"][in_assembly][obj_type]:
-                    nas_to_dict["Assemblies"][in_assembly][obj_type][object_id] = []
-            while pp < num_points:
-                start_pointer = start_pointer + word_length
-                if start_pointer >= 72:
-                    lk += 1
-                    line = input_lines[lk]
-                    start_pointer = 8
-                points.append(get_point(line, start_pointer, word_length))
-                pp += 1
-
-            if line_type in ["GRID", "GRID*"]:
-                nas_to_dict["PointsId"][grid_id] = input_pid
-                nas_to_dict["Points"].append([float(i) for i in points])
-                input_pid += 1
-            elif line_type in [
-                "CTRIA3",
-                "CTRIA3*",
-            ]:
-                tri = [nas_to_dict["PointsId"][int(i)] for i in points]
-                nas_to_dict["Assemblies"][in_assembly]["Triangles"][object_id].append(tri)
-            elif line_type in ["CROD", "CBEAM", "CBAR", "CROD*", "CBEAM*", "CBAR*"]:
-                tri = [nas_to_dict["PointsId"][int(i)] for i in points]
-                nas_to_dict["Assemblies"][in_assembly]["Lines"][object_id].append(tri)
-            elif line_type in ["CQUAD4", "CQUAD4*"]:
-                tri = [
-                    nas_to_dict["PointsId"][int(points[0])],
-                    nas_to_dict["PointsId"][int(points[1])],
-                    nas_to_dict["PointsId"][int(points[2])],
-                ]
-                nas_to_dict["Assemblies"][in_assembly]["Triangles"][object_id].append(tri)
-                tri = [
-                    nas_to_dict["PointsId"][int(points[0])],
-                    nas_to_dict["PointsId"][int(points[2])],
-                    nas_to_dict["PointsId"][int(points[3])],
-                ]
-                nas_to_dict["Assemblies"][in_assembly]["Triangles"][object_id].append(tri)
-            elif line_type in ["PSHELL", "PSHELL*"]:
-                nas_to_dict["Assemblies"][in_assembly]["Shells"][grid_id] = [str(object_id.strip()), points[0]]
-            elif line_type in ["MPC", "MPC*"]:
-                if (
-                    line_header
-                    and f"Port_{line_header.replace(',', '_')}_{object_id}"
-                    not in nas_to_dict["Assemblies"][in_assembly]["Triangles"]
-                ):
-                    name = f"Port_{line_header.replace(',', '_')}_{object_id}"
-                else:
-                    name = f"Port_{object_id}"
-                tri = [
-                    nas_to_dict["PointsId"][int(points[2])],
-                    nas_to_dict["PointsId"][int(points[7])],
-                    nas_to_dict["PointsId"][int(points[10])],
-                ]
-                nas_to_dict["Assemblies"][in_assembly]["Triangles"][name] = [tri]
-                tri = [
-                    nas_to_dict["PointsId"][int(points[2])],
-                    nas_to_dict["PointsId"][int(points[7])],
-                    nas_to_dict["PointsId"][int(points[15])],
-                ]
-                nas_to_dict["Assemblies"][in_assembly]["Triangles"][name].append(tri)
-                tri = [
-                    nas_to_dict["PointsId"][int(points[2])],
-                    nas_to_dict["PointsId"][int(points[10])],
-                    nas_to_dict["PointsId"][int(points[15])],
-                ]
-                nas_to_dict["Assemblies"][in_assembly]["Triangles"][name].append(tri)
-            elif line_type in ["CHEXA", "CHEXA*"]:
-
-                def add_hexa_tria(p1, p2, p3, hexa_obj):
-                    tri = [
-                        nas_to_dict["PointsId"][int(points[p1])],
-                        nas_to_dict["PointsId"][int(points[p2])],
-                        nas_to_dict["PointsId"][int(points[p3])],
-                    ]
-                    nas_to_dict["Assemblies"][in_assembly]["Solids"][hexa_obj].append(tri)
-
-                add_hexa_tria(0, 1, 2, object_id)
-                add_hexa_tria(0, 2, 3, object_id)
-                add_hexa_tria(0, 1, 4, object_id)
-                add_hexa_tria(1, 4, 5, object_id)
-                add_hexa_tria(1, 2, 6, object_id)
-                add_hexa_tria(1, 6, 5, object_id)
-                add_hexa_tria(4, 7, 6, object_id)
-                add_hexa_tria(4, 6, 5, object_id)
-                add_hexa_tria(0, 3, 7, object_id)
-                add_hexa_tria(0, 7, 4, object_id)
-                add_hexa_tria(3, 2, 7, object_id)
-                add_hexa_tria(2, 7, 6, object_id)
-            else:
-                from itertools import combinations
-
-                for k in list(combinations(points, 3)):
-                    tri = [
-                        nas_to_dict["PointsId"][int(k[0])],
-                        nas_to_dict["PointsId"][int(k[1])],
-                        nas_to_dict["PointsId"][int(k[2])],
-                    ]
-                    tri.sort()
-                    tri = tuple(tri)
-                    nas_to_dict["Assemblies"][in_assembly]["Solids"][object_id].append(tri)
-
-        return input_pid
-
-    logger.info("Loading file")
-    with open_file(file_path, "r") as f:
-        lines = f.read().splitlines()
-        for line in lines:
-            if line.startswith("INCLUDE"):
-                includes.append(line.split(" ")[1].replace("'", "").strip())
-        pid = parse_lines(lines)
-    for include in includes:
-        with open_file(os.path.join(os.path.dirname(file_path), include), "r") as f:
-            lines = f.read().splitlines()
-            name = include.split(".")[0]
-            pid = parse_lines(lines, pid, name)
-    logger.info("File loaded")
-    for assembly in list(nas_to_dict["Assemblies"].keys())[::]:
-        if (
-            nas_to_dict["Assemblies"][assembly]["Triangles"]
-            == nas_to_dict["Assemblies"][assembly]["Solids"]
-            == nas_to_dict["Assemblies"][assembly]["Lines"]
-            == {}
-        ):
-            del nas_to_dict["Assemblies"][assembly]
-    for _, assembly_object in nas_to_dict["Assemblies"].items():
-
-        def domino(segments):
-            def check_new_connection(s, polylines, exclude_index=-1):
-                s = s[:]
-                polylines = [poly[:] for poly in polylines]
-                attached = False
-                p_index = None
-                for i, p in enumerate(polylines):
-                    if i == exclude_index:
-                        continue
-                    if s[0] == p[-1]:
-                        p.extend(s[1:])  # the new segment attaches to the end
-                        attached = True
-                    elif s[-1] == p[0]:
-                        for item in reversed(s[:-1]):
-                            p.insert(0, item)  # the new segment attaches to the beginning
-                        attached = True
-                    elif s[0] == p[0]:
-                        for item in s[1:]:
-                            p.insert(0, item)  # the new segment attaches to the beginning in reverse order
-                        attached = True
-                    elif s[-1] == p[-1]:
-                        p.extend(s[-2::-1])  # the new segment attaches to the end in reverse order
-                        attached = True
-                    if attached:
-                        p_index = i
-                        break
-                if not attached:
-                    polylines.append(s)
-                return polylines, attached, p_index
-
-            polylines = []
-            for segment in segments:
-                polylines, attached_flag, attached_p_index = check_new_connection(segment, polylines)
-                if attached_flag:
-                    other_polylines = polylines[:attached_p_index] + polylines[attached_p_index + 1 :]
-                    polylines, _, _ = check_new_connection(
-                        polylines[attached_p_index], other_polylines, attached_p_index
-                    )
-
-            return polylines
-
-        def remove_self_intersections(polylines):
-            polylines = [poly[:] for poly in polylines]
-            new_polylines = []
-            for p in polylines:
-                if p[0] in p[1:]:
-                    new_polylines.append([p[0], p[1]])
-                    p.pop(0)
-                if p[-1] in p[:-1]:
-                    new_polylines.append([p[-2], p[-1]])
-                    p.pop(-1)
-                new_polylines.append(p)
-            return new_polylines
-
-        if assembly_object["Lines"]:
-            for lname, lines in assembly_object["Lines"].items():
-                new_lines = lines[::]
-                new_lines = remove_self_intersections(domino(new_lines))
-                assembly_object["Lines"][lname] = new_lines
-
-    return nas_to_dict
-
-
 @pyaedt_function_handler()
 @graphics_required
-def _write_stl(nas_to_dict, decimation, working_directory, enable_planar_merge=True):
-    """Write stl file."""
+def preview_pyvista(dict_in, decimation=0, output_stls=None):
     import pyvista as pv
 
-    logger = logging.getLogger("Global")
-
-    def _write_solid_stl(triangle, pp):
-        try:
-            # points = [nas_to_dict["Points"][id] for id in triangle]
-            points = [pp[i] for i in triangle[::-1]]
-        except KeyError:  # pragma: no cover
-            return
-        fc = points[0]
-        v1 = points[1]
-        v2 = points[2]
-        cv1 = GeometryOperators.v_points(fc, v2)
-        cv2 = GeometryOperators.v_points(fc, v1)
-        try:
-            n = GeometryOperators.v_cross(cv1, cv2)
-
-            normal = GeometryOperators.normalize_vector(n)
-            f.write(f" facet normal {normal[0]} {normal[1]} {normal[2]}\n")
-            f.write("  outer loop\n")
-            f.write(f"   vertex {points[0][0]} {points[0][1]} {points[0][2]}\n")
-            f.write(f"   vertex {points[1][0]} {points[1][1]} {points[1][2]}\n")
-            f.write(f"   vertex {points[2][0]} {points[2][1]} {points[2][2]}\n")
-            f.write("  endloop\n")
-            f.write(" endfacet\n")
-        except Exception:  # pragma: no cover
-            logger.debug("Failed to normalize vector.")
-
-    logger.info("Creating STL file with detected faces")
-    enable_stl_merge = False if enable_planar_merge == "False" or enable_planar_merge is False else True
-
-    def decimate(points_in, faces_in):
-        fin = [[3] + list(i) for i in faces_in]
-        mesh = pv.PolyData(points_in, faces=fin)
-        new_mesh = mesh.decimate_pro(decimation, preserve_topology=True, boundary_vertex_deletion=False)
-        points_out = list(new_mesh.points)
-        faces_out = [i[1:] for i in new_mesh.faces.reshape(-1, 4) if i[0] == 3]
-        return points_out, faces_out
-
-    output_stls = []
-    for assembly_name, assembly in nas_to_dict["Assemblies"].items():
-        output_stl = os.path.join(working_directory, assembly_name + ".stl")
-        f = open(output_stl, "w")
-        for tri_id, triangles in assembly["Triangles"].items():
+    if decimation > 0:
+        pl = pv.Plotter(shape=(1, 2))
+    else:  # pragma: no cover
+        pl = pv.Plotter()
+    dargs = dict(show_edges=True)
+    colors = []
+    color_by_assembly = True
+    if len(dict_in["Assemblies"]) == 1:
+        color_by_assembly = False
+
+    css4_colors = list(CSS4_COLORS.values())
+    k = 0
+    p_out = dict_in["Points"][::]
+    for assembly in dict_in["Assemblies"].values():
+        if color_by_assembly:
+            h = css4_colors[k].lstrip("#")
+            colors.append(tuple(int(h[i : i + 2], 16) for i in (0, 2, 4)))
+            k += 1
+
+        for triangles in assembly["Triangles"].values():
+            if not triangles:
+                continue
             tri_out = triangles
-            p_out = nas_to_dict["Points"][::]
-            if decimation > 0 and len(triangles) > 20:
-                p_out, tri_out = decimate(nas_to_dict["Points"], tri_out)
-            f.write(f"solid Sheet_{tri_id}\n")
-            if enable_planar_merge == "Auto" and len(tri_out) > 50000:
-                enable_stl_merge = False  # pragma: no cover
-            for triangle in tri_out:
-                _write_solid_stl(triangle, p_out)
-            f.write("endsolid\n")
-        for solidid, solid_triangles in assembly["Solids"].items():
-            f.write(f"solid Solid_{solidid}\n")
+            fin = [[3] + list(i) for i in tri_out]
+            if not color_by_assembly:
+                h = css4_colors[k].lstrip("#")
+                colors.append(tuple(int(h[i : i + 2], 16) for i in (0, 2, 4)))
+                k = k + 1 if k < len(css4_colors) - 1 else 0
+            pl.add_mesh(pv.PolyData(p_out, faces=fin), color=colors[-1], **dargs)
+
+        for triangles in assembly["Solids"].values():
+            if not triangles:
+                continue
             import pandas as pd
 
-            df = pd.Series(solid_triangles)
+            df = pd.Series(triangles)
             tri_out = df.drop_duplicates(keep=False).to_list()
-            p_out = nas_to_dict["Points"][::]
-            if decimation > 0 and len(solid_triangles) > 20:
-                p_out, tri_out = decimate(nas_to_dict["Points"], tri_out)
-            if enable_planar_merge == "Auto" and len(tri_out) > 50000:
-                enable_stl_merge = False  # pragma: no cover
-            for triangle in tri_out:
-                _write_solid_stl(triangle, p_out)
-            f.write("endsolid\n")
-        f.close()
-        output_stls.append(output_stl)
-        logger.info("STL file created")
-    return output_stls, enable_stl_merge
-
+            p_out = dict_in["Points"][::]
+            fin = [[3] + list(i) for i in tri_out]
+            if not color_by_assembly:
+                h = css4_colors[k].lstrip("#")
+                colors.append(tuple(int(h[i : i + 2], 16) for i in (0, 2, 4)))
+                k = k + 1 if k < len(css4_colors) - 1 else 0
 
-@pyaedt_function_handler()
-@graphics_required
-def nastran_to_stl(input_file, output_folder=None, decimation=0, enable_planar_merge="True", preview=False):
-    """Convert Nastran file into stl."""
-    import pyvista as pv
+            pl.add_mesh(pv.PolyData(p_out, faces=fin), color=colors[-1], **dargs)
 
-    if not Path(input_file).exists():
-        raise FileNotFoundError(f"File ({input_file}) not found")
+    pl.add_text("Input mesh", font_size=24)
+    pl.reset_camera()
 
-    logger = logging.getLogger("Global")
-    nas_to_dict = _parse_nastran(input_file)
-
-    empty = True
-    for assembly in nas_to_dict["Assemblies"].values():
-        if assembly["Triangles"] or assembly["Solids"] or assembly["Lines"]:
-            empty = False
-            break
-    if empty:  # pragma: no cover
-        logger.error("Failed to import file. Check the model and retry")
-        return False
-    if output_folder is None:
-        output_folder = os.path.dirname(input_file)
-    output_stls, enable_stl_merge = _write_stl(nas_to_dict, decimation, output_folder, enable_planar_merge)
-    if preview:
-        logger.info("Generating preview...")
-        if decimation > 0:
-            pl = pv.Plotter(shape=(1, 2))
-        else:  # pragma: no cover
-            pl = pv.Plotter()
-        dargs = dict(show_edges=True)
-        colors = []
-        color_by_assembly = True
-        if len(nas_to_dict["Assemblies"]) == 1:
-            color_by_assembly = False
-
-        def preview_pyvista(dict_in):
-            css4_colors = list(CSS4_COLORS.values())
-            k = 0
-            p_out = nas_to_dict["Points"][::]
-            for assembly in dict_in["Assemblies"].values():
-                if color_by_assembly:
-                    h = css4_colors[k].lstrip("#")
-                    colors.append(tuple(int(h[i : i + 2], 16) for i in (0, 2, 4)))
-                    k += 1
-
-                for triangles in assembly["Triangles"].values():
-                    if not triangles:
-                        continue
-                    tri_out = triangles
-                    fin = [[3] + list(i) for i in tri_out]
-                    if not color_by_assembly:
-                        h = css4_colors[k].lstrip("#")
-                        colors.append(tuple(int(h[i : i + 2], 16) for i in (0, 2, 4)))
-                        k = k + 1 if k < len(css4_colors) - 1 else 0
-                    pl.add_mesh(pv.PolyData(p_out, faces=fin), color=colors[-1], **dargs)
-
-                for triangles in assembly["Solids"].values():
-                    if not triangles:
-                        continue
-                    import pandas as pd
-
-                    df = pd.Series(triangles)
-                    tri_out = df.drop_duplicates(keep=False).to_list()
-                    p_out = nas_to_dict["Points"][::]
-                    fin = [[3] + list(i) for i in tri_out]
-                    if not color_by_assembly:
-                        h = css4_colors[k].lstrip("#")
-                        colors.append(tuple(int(h[i : i + 2], 16) for i in (0, 2, 4)))
-                        k = k + 1 if k < len(css4_colors) - 1 else 0
-
-                    pl.add_mesh(pv.PolyData(p_out, faces=fin), color=colors[-1], **dargs)
-
-        preview_pyvista(nas_to_dict)
-        pl.add_text("Input mesh", font_size=24)
+    if decimation > 0 and output_stls:
+        k = 0
         pl.reset_camera()
-        if decimation > 0 and output_stls:
-            k = 0
-            pl.reset_camera()
-            pl.subplot(0, 1)
-            css4_colors = list(CSS4_COLORS.values())
-            for output_stl in output_stls:
-                mesh = pv.read(output_stl)
-                h = css4_colors[k].lstrip("#")
-                colors.append(tuple(int(h[i : i + 2], 16) for i in (0, 2, 4)))
-                pl.add_mesh(mesh, color=colors[-1], **dargs)
-                k = k + 1 if k < len(css4_colors) - 1 else 0
-            pl.add_text("Decimated mesh", font_size=24)
-            pl.reset_camera()
-            pl.link_views()
-        if "PYTEST_CURRENT_TEST" not in os.environ:
-            pl.show()  # pragma: no cover
-    logger.info("STL files created")
-    return output_stls, nas_to_dict, enable_stl_merge
+        pl.subplot(0, 1)
+        css4_colors = list(CSS4_COLORS.values())
+        for output_stl in output_stls:
+            mesh = pv.read(output_stl)
+            h = css4_colors[k].lstrip("#")
+            colors.append(tuple(int(h[i : i + 2], 16) for i in (0, 2, 4)))
+            pl.add_mesh(mesh, color=colors[-1], **dargs)
+            k = k + 1 if k < len(css4_colors) - 1 else 0
+        pl.add_text("Decimated mesh", font_size=24)
+        pl.reset_camera()
+        pl.link_views()
+    if "PYTEST_CURRENT_TEST" not in os.environ:
+        pl.show()  # pragma: no cover
 
 
 @pyaedt_function_handler()
 @graphics_required
-def simplify_stl(input_file, output_file=None, decimation=0.5, preview=False):
+def simplify_and_preview_stl(input_file, output_file=None, decimation=0.5, preview=False):
     """Import and simplify a stl file using pyvista and fast-simplification.
 
     Parameters
diff --git a/tests/system/extensions/test_45_extensions.py b/tests/system/extensions/test_45_extensions.py
index c04cab406ef..b88891b637d 100644
--- a/tests/system/extensions/test_45_extensions.py
+++ b/tests/system/extensions/test_45_extensions.py
@@ -135,7 +135,16 @@ def test_06_project_import_stl(self, add_app, local_scratch):
             os.path.join(local_scratch.path, "sphere.stl"),
         )
 
-        assert main({"is_test": True, "file_path": file_path, "lightweight": True, "decimate": 0.0, "planar": True})
+        assert main(
+            {
+                "is_test": True,
+                "file_path": file_path,
+                "lightweight": True,
+                "decimate": 0.0,
+                "planar": True,
+                "remove_multiple_connections": True,
+            }
+        )
 
         assert len(aedtapp.modeler.object_list) == 1
         aedtapp.close_project(aedtapp.project_name)
diff --git a/tests/system/general/test_20_HFSS.py b/tests/system/general/test_20_HFSS.py
index e2750259b95..9d0adf34421 100644
--- a/tests/system/general/test_20_HFSS.py
+++ b/tests/system/general/test_20_HFSS.py
@@ -1466,11 +1466,11 @@ def test_59_test_nastran(self):
         assert self.aedtapp.modeler.import_nastran(example_project2, decimation=0.1, preview=True, save_only_stl=True)
         assert self.aedtapp.modeler.import_nastran(example_project2, decimation=0.5)
         example_project = os.path.join(TESTS_GENERAL_PATH, "example_models", test_subfolder, "sphere.stl")
-        from ansys.aedt.core.visualization.advanced.misc import simplify_stl
+        from ansys.aedt.core.visualization.advanced.misc import simplify_and_preview_stl
 
-        out = simplify_stl(example_project, decimation=0.8)
+        out = simplify_and_preview_stl(example_project, decimation=0.8)
         assert os.path.exists(out)
-        out = simplify_stl(example_project, decimation=0.8, preview=True)
+        out = simplify_and_preview_stl(example_project, decimation=0.8, preview=True)
         assert out
 
     def test_60_set_variable(self):
diff --git a/tests/system/general/test_utils.py b/tests/system/general/test_utils.py
index 92ebdaf1d05..01ad0ab8132 100644
--- a/tests/system/general/test_utils.py
+++ b/tests/system/general/test_utils.py
@@ -52,9 +52,9 @@ def test_settings_load_default_yaml():
     assert default_settings_attributes == local_settings_attributes
 
 
-def test_settings_writte_default_yaml(tmp_path):
+def test_settings_write_default_yaml(tmp_path):
     default_settings = Settings()
     path = str("pyaedt_settings.yaml")
-    default_settings.writte_yaml_configuration(path)
+    default_settings.write_yaml_configuration(path)
 
     assert os.path.exists(path)
diff --git a/tests/unit/extensions/test_import_nastran.py b/tests/unit/extensions/test_import_nastran.py
index 3948b44f3bd..3ade263de91 100644
--- a/tests/unit/extensions/test_import_nastran.py
+++ b/tests/unit/extensions/test_import_nastran.py
@@ -73,8 +73,8 @@ def test_import_nastran_default_values():
 
 @patch("tkinter.filedialog.askopenfilename")
 def test_import_nastran_modified_values(mock_askopenfilename):
-    """Test that the modifief values of the UI are returned correctly."""
-    EXPECTED_RESULT = ExtensionData(0.5, True, False, MOCK_NAS_PATH)
+    """Test that the modified values of the UI are returned correctly."""
+    EXPECTED_RESULT = ExtensionData(0.5, True, False, MOCK_NAS_PATH, True)
     mock_askopenfilename.return_value = MOCK_NAS_PATH
 
     root = create_ui(withdraw=True)
@@ -82,6 +82,7 @@ def test_import_nastran_modified_values(mock_askopenfilename):
     root.nametowidget("browse_button").invoke()
     root.nametowidget("check_lightweight").invoke()
     root.nametowidget("check_planar_merge").invoke()
+    root.nametowidget("check_remove_multiple_connections").invoke()
     root.nametowidget("decimation_text").delete("1.0", "end")
     root.nametowidget("decimation_text").insert("1.0", "0.5")
     root.nametowidget("ok_button").invoke()
@@ -94,7 +95,7 @@ def test_import_nastran_modified_values(mock_askopenfilename):
 @pytest.mark.parametrize("mock_path", [MOCK_NAS_PATH, MOCK_STL_PATH])
 @patch("tkinter.filedialog.askopenfilename")
 def test_import_nastran_preview_on_non_existing_file(mock_askopenfilename, mock_path):
-    """Test that the preview button raises an exception when non existing file is selected."""
+    """Test that the preview button raises an exception when a non-existing file is selected."""
     mock_askopenfilename.return_value = mock_path
     root = create_ui(withdraw=True)
     root.nametowidget("browse_button").invoke()