Design Nomenclature / Digital Model Making
STEP
Also called .step, .stp, ISO 10303, AP214, AP242, IGES
This entry has not been translated yet and is shown in English.
An open ISO-standardized CAD exchange format carrying exact B-rep geometry — trimmed spline surfaces, topology, assemblies, units, and in AP242 tolerances and annotation. It has no feature history: you receive an exact solid you can measure and machine, not one you can rebuild by changing a dimension. IGES is its older, surfaces-only ancestor.
In practice
The answer to “send it to the machinist”. Anyone asking for an STL of a CAD model is asking for a tessellation of this, and throwing away the exactness that made it worth having.
Not to be confused with
- STLAn unstructured list of triangles, each written as three vertices and a normal. That is all: no units, no scale, no colour, no materials, no assemblies, no curves, and no shared vertices — a point is repeated once per triangle touching it. Nothing in the format requires the triangles to form a closed solid.
- OBJA plain-text mesh format carrying vertices, faces of any size, UVs, normals, and material references in a sidecar .mtl file. No animation, no rig, no scene hierarchy, no unit convention. Ubiquitous because it is trivial to parse and everything reads it — not because it is good at anything.