STEP (STandard for the Exchange of Product model data) is a CAD data exchange format defined by ISO 10303. Files carry the extension .step or .stp. They contain a neutral 3D model, independent of the software that created it: a file produced in one CAD system opens in another, including in workshops’ CAM software.
A STEP file describes the exact geometry of the solid, with mathematically defined surfaces: it does not approximate it with triangles as the STL used in 3D printing does. Depending on the application protocol used (AP203, AP214, AP242), it can also carry the structure of an assembly, colours or dimensioning annotations (PMI). It advantageously replaces IGES, which is older and more prone to unjoined surfaces, and differs from DXF, a 2D drawing format used for sheet metal cutting.
For machining, the workshop imports the STEP file, prepares its toolpaths, estimates the volume of material to remove and quotes faster. The file is rarely sufficient on its own: it does not carry, or not reliably, the tolerances, material, roughness or treatments, which appear on the definition drawing. An export in the wrong unit (inches instead of millimetres) remains a frequent error: check it before sending.
In a quote request
Export one part per file, as a complete, closed solid (no open surfaces or overlapping bodies), in millimetres, with the reference and revision in the name. Always attach the corresponding dimensioned PDF, which is authoritative for tolerances unless stated otherwise. For sheet metal to be cut, add a DXF flat pattern; for 3D printing, an STL or 3MF may be requested. The guide on CAD file formats goes through each case.