Exchange · 5 min read
A STEP file is an exchange format for 3D models that almost every CAD package can read and write, defined in ISO 10303. It contains the geometry and, with AP214 and AP242, also the assembly structure with part names and quantities. What is not in it is your model history: features, sketches and parameters stay behind in your own package.
Published 21 September 2026
In short
01 On this page
A STEP describes the shape of each part as an exact mathematical description of faces and edges, not as triangles. That is why you can still carry on with it in any package: measuring, making sections, editing.
The file also contains the product structure: which parts hang under which assembly, how often they occur and where they are. Some exports also include material, density and colour.
Your model history. Features, sketches, parameters and relations stay in your own CAD package. Someone who opens the STEP gets the end result, not the way you got there.
That is not a shortcoming but a choice: precisely because of it every package can read it. If you want to exchange parametrically, you need the original file.
Practical consequence: you always make changes in the original model and then export again. Repairing a STEP is almost never the right route.
STEP has different application protocols. In practice you come across three.
AP214 or AP242. Both contain the assembly structure with parts and quantities, and that is what you need to get a BOM out of it and to check the model.
If you do not know what the recipient can handle, AP214 is the safe choice. If you want to send dimensioning and tolerances in the model, AP242 is the only option, but then check whether the recipient can do anything with it.
The settings differ per package, but the rules of thumb are the same everywhere.
With BOMproof
BOMproof puts your STEP model, your PDF drawings and your Excel BOM side by side and points out every deviation: with a pin in the 3D model and a balloon on the drawing. You tick off what is correct.
Method and corrections
This guide describes in our own words how we carry out a check ourselves. We refer to standards by number; the literal text of the standard is not reproduced here, because it is protected by copyright. Found a mistake? Email info@bomproof.nl: we correct it within a week and put the new date at the top.
02 Frequently asked questions
Yes. This site has a free STEP viewer that opens the file in your own browser: 3D model, product structure and BOM. The file is not uploaded.
Only the extension. The content is the same and both start with the line ISO-10303-21.
Because it is readable text and every face and every edge is described separately. A design of hundreds of parts easily runs to tens or hundreds of megabytes. Zipping helps a lot, because text compresses well.
03 Knowledge base
Book a 30-minute demo. Bring one of your own designs and see live how BOMproof checks it.