3D model
A STEP without assembly structure.
You open the STEP and see one big lump of geometry, or a long list of nameless parts without assemblies around them. Then you cannot get a BOM out of it and there is little to check.
Published 21 September 2026
01 What it is
STEP without structure, briefly explained.
A usable STEP contains the product structure: the design, the subassemblies, the parts below them and how often each part occurs. That structure is what makes a BOM possible.
With an export without structure everything ends up on one level, sometimes even as one merged whole. The geometry is then still right, but quantities and names are gone.
How you notice it
- No tree, only a list of parts
- Parts with names like Solid1, Part1 or a number
- One part that is the whole design
- No quantities to be determined
In a check
This shows up as caution in the check of the 3D model. You judge what has to be done about it.
02 Example
What it looks like.
Example export GRP-2210 (demo)
- Parts in the file
- 46
- Assemblies
- none
- Names
- Solid1 through Solid46
- BOM can be made
- no
The geometry is complete and you can view and measure the model, but there is no way to know which part is what and how often it occurs.
How it comes about
- An export setting that merges the design into one whole
- Exporting from a view or a simplified representation
- An older STEP version or a setting without product structure
- An export from a viewer or conversion tool instead of from the CAD package itself
03 Approach
Find, fix, prevent.
How to find it
You see it straight away on opening: is there a tree with assemblies and part names, or not? The free viewer shows the product structure as it is in the file.
- 1 Open the STEP in the free viewer.
- 2 See whether there is a product structure with assemblies and part names.
- 3 Check whether the quantities per part match what you expect.
- 4 If there is no structure, export again with the right setting.
Fix
- Export again from the CAD package itself, with the assembly structure switched on.
- Choose AP214 or AP242, because those contain the product structure.
- Export the design as one file with the parts in it, not as separate files, unless the recipient asks for that.
- Make sure the part names or file names come along, otherwise matching to the BOM remains impossible.
Prevent
- Record one export setting per CAD package and always use it.
- Open the export once in a viewer before you send it.
- Export the STEP and the BOM in the same action.
With BOMproof
Every release, without having to think about it.
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.
04 Frequently asked questions
STEP without structure.
01 Which STEP version should I choose?
AP214 or AP242. Both contain the product structure with assemblies, parts and quantities. AP203 is possible too, but contains less, for example no colours.
02 Can I add the structure afterwards?
Not meaningfully. The information is not in the file, so you would be rebuilding it by hand. Exporting again is faster and more reliable.
03 Where do I find the settings for my package?
For each CAD package this site has a page with the export steps and the pitfalls, from SOLIDWORKS and Inventor to NX, Creo, CATIA, Solid Edge, Fusion and Onshape.
05 Often seen together
Other errors from the same corner.
You never want to hunt for this error by hand again.
Upload your model, your drawings and your BOM and let BOMproof check them against each other. Book a demo with your own design.