STEP file

A STEP file (STEP stands for Standard for the Exchange of Product model data, ISO 10303) is the industry standard for exchanging 3D CAD data between different software systems. The files have the .step or .stp extension and contain the exact solid or surface geometry of a 3D model in a neutral format that practically any CAD system can read.

In mechanical engineering, STEP is the de facto standard for handing CAD data between designers and manufacturers. Unlike native formats (such as .sldprt for SolidWorks or .ipt for Inventor), a STEP file opens in any CAD software, and you do not need a license for the program the model was created in.

There are several STEP application protocols. The most common are AP203 and AP214 for mechanical parts and assemblies. AP242 is a newer protocol that can also carry manufacturing information, including geometric tolerances (GD&T, PMI) and the product structure.

The limitation of STEP is that transfer of the model's parameters and feature history is not guaranteed. A STEP file usually stores "frozen" geometry without editable parameters. For collaboration in which the model has to be modified further, a native format is the better choice.

STEP is the default choice whenever you send 3D data to someone outside your own CAD system: to a manufacturer for quoting and CNC programming, to a mold maker, to a partner design team or to a customer who needs to fit the part into their product. It preserves exact geometry better than mesh formats such as STL, which replace surfaces with triangles.

It is also well suited to archiving released versions of parts, because it depends less on a particular software version, and to importing standard and purchased components from their manufacturers (bearings, drives, connectors).

Always send a drawing with a STEP file, or at least a specification of tolerances, material and surface finishes. The common AP203 and AP214 protocols do not carry this information, and without it the manufacturer has no way of knowing which dimensions are critical.

Check the file after export. In assemblies, part names or colors can get lost, and units can be misinterpreted (millimeters versus inches). Complex surfaces sometimes import with gaps. If the recipient needs to modify the model further, agree whether a native format would be better, because editing "dumb" geometry from a STEP file takes more work.