What is a PRT file?
PRT is short for "part". In mechanical CAD, a .prt file holds the definition of a component: its solid and surface geometry, the feature history used to build it, sketches, datums, materials, colors and product manufacturing information. Over the years, several CAD systems have used the extension, but today it almost always refers to a Siemens NX or PTC Creo file.
Because the extension alone does not say which system created a file, the first step when receiving a .prt is to identify its origin. Creo files are often followed by a version number, such as .prt.1 or .prt.2, while NX files are not. Software built to read one variant generally cannot open the other. For a broader overview of part files, see our part file format page.
NX PRT vs. Creo PRT
| Feature | Siemens NX | PTC Creo / Pro/ENGINEER |
| History | Formerly Unigraphics | Formerly Pro/ENGINEER and Wildfire |
| Geometric kernel | Parasolid | PTC's own kernel |
| Assemblies | Stored in .prt files as well, parts and assemblies share the extension | Stored in separate .asm files |
| File naming | Plain .prt extension | Often followed by a version number (.prt.1, .prt.2) |
| Configurations | Reference sets | Family tables and simplified representations |
What Is PRT Used For? Applications and Industry Use Cases
NX and Creo are among the leading high-end CAD systems in automotive, aerospace, industrial machinery and consumer products, so PRT files are central to the supply chains of these industries. They carry not only geometry, but also the PMI, holes, threads and other manufacturing information that downstream teams rely on.
For software developers, reading PRT files lets CAD, CAM, CAE, metrology, PDM/PLM and visualization applications work directly with native NX and Creo data, instead of asking customers to export neutral files. Persistent names keep topology identifiers stable across design iterations, which reduces manual updates in simulation and machining workflows.
Challenges or Common Pitfalls
Confusing the two PRT families is the first pitfall. A file sent as "the .prt" may come from NX or from Creo, and an application has to detect which one before choosing the right reader.
Both formats are proprietary and evolve with every release of their CAD system, so a reader must be updated constantly. Some content is also hard to carry over: Creo family tables require their .xpr and .xas accelerator files, Creo 8.0 monolithic assemblies use a dedicated structure, and parametric feature trees are specific to the original CAD system.
Finally, translating NX and Creo data into another environment usually means working with exact B-rep geometry and attributes rather than editable features. Projects that expect to keep a live feature history after translation should plan for that difference.
How Spatial Helps
Our 3D InterOp SDK imports both NX and Creo PRT files without requiring an NX or Creo license, and delivers exact B-rep geometry to CGM Modeler, 3D ACIS Modeler or Parasolid. For NX, you can use your own Parasolid libraries or our built-in Parasolid Direct implementation, which needs no setup. For Creo, 3D InterOp reads Pro/ENGINEER, Wildfire and Creo files.
3D InterOp extracts the full assembly tree, with instance color, transparency and suppression, along with persistent IDs and persistent names, sheet bodies, free curves, workplanes, layers, coordinate systems, material and user properties, and document information such as units and version. Compressed NX files are supported, and Creo family tables, simplified representations and user parameters are read as well.
For downstream manufacturing and inspection, 3D InterOp imports semantic PMI from both formats, including notes, dimensions, geometric tolerances and datums, plus hole and thread data, and visualization data. NX and Creo files are imported only; writing them is not supported.