What is a .sldprt file?

What a SolidWorks part contains

Two things, and it helps to keep them apart. The first is the finished solid: faces, edges and vertices in the boundary representation of the Parasolid kernel, which is exactly what a STEP or Parasolid export carries away. The second is how it got there: the sketches, the extrudes, cuts, fillets, patterns and their dimensions, stacked in the order they were applied. SolidWorks calls that stack the FeatureManager design tree, and it is the reason a SolidWorks user can change a hole diameter and have everything downstream update.

Everything an importer in another system receives is the first thing. The tree stays behind, because no other application can replay SolidWorks features. Fusion, Inventor, Onshape, Creo and Rhino all import SolidWorks parts as plain solids for that reason, and a "convert SLDPRT to STEP" request is really a request for the solid without the tree.

The document also carries its units, set per document, plus material, appearance colours, custom properties, configurations (named variants of the same part with different dimensions suppressed or changed), and often a saved preview image.

The three sibling files

A SolidWorks design is usually three files. The part is .sldprt. An assembly, .sldasm, holds no geometry of its own; it references part files by path and records how they are mated together. A drawing, .slddrw, references either. Send an assembly without its parts and the recipient opens an empty tree with missing-file warnings. SolidWorks ships a Pack and Go command that gathers all the references into one folder or zip for exactly this reason.

Versions

SolidWorks is not backward compatible, and this is the single most common reason a file will not open. A part saved in SolidWorks 2025 opens in 2025 and later. It does not open in 2024, and there is no "save as older version" option. The Service Pack releases within a year are compatible with each other.

The way around it is a neutral export from the newer installation: STEP AP214 or AP242 for most purposes, or Parasolid for another Parasolid-based system, which keeps the geometry exact down to the kernel's tolerance.

Where these files come from

Mechanical engineering and product design, in the small and mid-sized company range where SolidWorks is the default. Supplier catalogues from McMaster-Carr, Misumi and the bearing and fastener manufacturers offer SLDPRT downloads alongside STEP. Student work is common too, since the education licence is widespread.

Getting geometry out

From inside SolidWorks: Save As, and pick STEP, Parasolid, IGES, STL or 3MF. For a print, the STL export dialog has a resolution setting; leave the default and curved surfaces come out visibly faceted, so set it to fine or custom. For CAD exchange, STEP AP242 carries colours and, if the model has them, the annotations.

Without SolidWorks, the free eDrawings viewer opens the part for viewing and measuring but exports only images. Onshape's free plan imports the part in a browser and exports STEP from it, which is the practical no-cost route from an SLDPRT to something this site can open, provided a public document is acceptable. Fusion imports it too, on a commercial subscription.

How to open a .sldprt file

eDrawings is the free way. It opens SolidWorks parts and assemblies on Windows and macOS with measurement and sectioning, and it cannot edit or save them. Onshape's free plan imports a .sldprt in a browser. This site cannot read the format.

To edit the model with its feature history, you need SolidWorks itself, on Windows. Fusion and Inventor import SolidWorks parts as geometry; the feature tree does not come with them.

Version is the wall. A file saved in SolidWorks 2025 will not open in SolidWorks 2024 or anything earlier, and there is no "save as older version". The sender has to export STEP or Parasolid instead. For a part on its own that costs nothing but the history; for an assembly, ask for the .sldasm and every referenced part, or a single STEP.