CAD File Formats 101
STEP, STL, IGES, DXF, Parasolid and more — which to upload and why
CAD files exchange geometry in two flavors: boundary representation (B-rep, exact: STEP, IGES, Parasolid, native CAD) and tessellated (facets: STL, 3MF). For quoting and manufacturing, STEP is the universal choice — exact geometry, no mesh approximation, wide support. STL is fine for 3D printing; DXF is 2D; native formats carry features but lock you to one vendor.
1. The format families
B-rep formats (STEP AP203/AP214, IGES, Parasolid X_T, 3DM, CATPART, SLDPRT, PRT, SAT) describe exact surfaces and edges — perfect for CNC, sheet and molding where dimensions must be exact. AP214 adds colors, layers and product data; AP203 is geometry-only.
Tessellated formats (STL, 3MF, OBJ) approximate surfaces with triangles: adequate for 3D printing (the printer slices facets anyway) but lossy for machined parts — a fine fillet becomes a faceted edge. 3MF adds color, lattice and units.
2. What the platform accepts
14 formats: STEP (.step/.stp), IGES (.igs/.iges), Parasolid (.x_t/.x_b), SolidWorks (.sldprt), SolidEdge, NX (.prt), CATIA (.catanalysis? .catpart), Rhino (.3dm), ACIS (.sat), Inventor (.ipt), JT, 3MF, STL and DXF (2D for sheet/laser).
Preferred: STEP for any machined/molded/sheet part; STL or 3MF for 3D printing; DXF with thickness note for laser-cut sheet. Upload one file per part or a zipped assembly.
3. Upload quality checklist
Check units (mm vs inch — state on the drawing), scale (a 100× scaled part quotes 100× wrong), watertightness (for printing: no open shells — most CAD exports are solid, scanned/mesh files often are not), and file size (keep under ~200 MB; simplify assemblies).
Remove non-manufacturing data (reference bodies, sketches, mates) — they confuse dimension extraction — and set the coordinate system to the datum scheme you want measured.
4. If your format is missing
Most CAD packages export STEP natively (File → Save As → STEP AP214); if not, use a free converter (CAD viewer exporters, online converters for simple parts — mind confidentiality on proprietary designs).
When geometry-only is not enough (colors for overmolding, texture, PMI tolerances), attach the drawing/PDF with the model and reference it on the PO.
Quick reference
| Format | Type | Best for | Notes |
|---|---|---|---|
| STEP AP203/214 | B-rep exact | CNC, sheet, molding | Universal choice |
| IGES | B-rep exact | Legacy exchange | Older, larger files |
| Parasolid X_T | B-rep exact | NX/SolidWorks exchange | Exact geometry |
| STL | Tessellated | 3D printing | Faceted, lossy |
| 3MF | Tessellated+ | 3D printing, color | Modern print format |
| DXF | 2D vector | Laser/sheet cutting | 2D only |
| Native (SLDPRT etc.) | B-rep exact | Vendor-specific | Carries features |
Sources & references
- ISO 10303 — STEP standard
- Xometry Learning Center — CAD File Formats (public engineering reference)