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STEP AP203 vs AP214 vs AP242: Which One Should You Export?
AP203, AP214 and AP242 are three versions of the STEP standard, and all three carry the same exact solid geometry. They differ in what travels with it: AP214 adds colours and layers, and AP242 adds machine-readable annotations. For a single part going to a machine shop or an instant-quote site, export AP214.
What is the difference between AP203, AP214 and AP242?
They are application protocols of ISO 10303, the STEP standard. AP203 came from aerospace and defence design, AP214 from the automotive industry, and AP242 merges the two and adds annotations and other model-based data. The solid geometry is the same in all three.
STEP is not one format but a family. Each application protocol (AP) defines which kinds of data a file may contain for a particular industry. The three that matter for mechanical parts compare like this:
| Compared on | AP203 | AP214 | AP242 |
|---|---|---|---|
| Full name | Configuration controlled 3D design | Core data for automotive mechanical design | Managed model-based 3D engineering |
| Published | 1994 (2nd edition 2011) | 2001 (later editions to 2010) | 2014 (2nd edition 2020) |
| Exact solid geometry | Yes: Yes | Yes: Yes | Yes: Yes |
| Assemblies | Yes: Yes | Yes: Yes | Yes: Yes |
| Colours and layers | No: Not in the 1st edition most tools write | Yes: Yes | Yes: Yes |
| Machine-readable GD&T (PMI) | No: No | No: Display only, in later editions | Yes: Yes |
| Support in CAD, CAM and quoting tools | Universal | Universal | Most current tools |
| Header FILE_SCHEMA | CONFIG_CONTROL_DESIGN | AUTOMOTIVE_DESIGN | AP242_MANAGED_MODEL_BASED_3D_ENGINEERING… |
For background on the format itself, see what a STEP file is.
Does the STEP version change the geometry of my part?
No. A bracket exported as AP203, AP214 or AP242 has the same faces, edges and dimensions in every case, because all three store the same exact B-rep solid. Switching protocol changes only the extra data, such as colours, layers and annotations.
The geometry part of STEP is shared across protocols: planes, cylinders, cones, spline surfaces and the topology that joins them into a closed solid. A 12 mm hole is a 12 mm cylinder in all three. That is why a machine shop rarely cares which one you pick, and why the wrong choice almost never ruins a quote.
What can go missing is everything around the solid. Export AP203 from a model with colour-coded faces and the colours are dropped. Export anything other than AP242 and the tolerances you attached to faces in CAD do not travel as data, so they still need to be on a drawing.
Which STEP version should I send to a machine shop?
Send AP214 unless the shop asks for something else. Every CAM program and instant-quote site reads it, it keeps face colours that some shops use to flag threaded or finished surfaces, and it avoids the occasional AP242 import problem in older software.
Instant-quote pricing engines read the solid to measure volume, stock size and features, so for them any of the three works. The protocol matters more when a person opens the file: colours that mark threaded holes or critical faces survive in AP214 and AP242 but not in a first-edition AP203 file.
Two more things matter more than the protocol. Export a single solid per part, not a surface model, and keep the tolerances and finishes on a PDF drawing that goes with the STEP. Our guide to the best file format for a machine shop covers the rest.
How do I tell which AP a STEP file uses?
Open the .step or .stp file in any plain text editor and find the FILE_SCHEMA line in the header, within the first few lines. The schema name tells you the protocol: CONFIG_CONTROL_DESIGN is AP203, AUTOMOTIVE_DESIGN is AP214, and AP242_MANAGED_MODEL_BASED is AP242.
A STEP file is plain text. The header of an AP214 file looks like this:
ISO-10303-21;
HEADER;
FILE_DESCRIPTION(('bracket'),'2;1');
FILE_NAME('bracket.step','2026-10-02T09:14:55',('Author'),(''),
'CAD export','CAD system','');
FILE_SCHEMA(('AUTOMOTIVE_DESIGN { 1 0 10303 214 1 1 1 1 }'));
ENDSEC;The number inside the braces repeats the protocol: 10303 214 is ISO 10303-214. An AP203 file reads CONFIG_CONTROL_DESIGN, and an AP242 file reads AP242_MANAGED_MODEL_BASED_3D_ENGINEERING_MIM_LF. A second-edition AP203 file spells its full name out the same way.
When should I use AP242 instead?
Use AP242 when tolerances, datums and surface finish need to travel inside the model as data a program can read, for example in a model-based definition workflow with no drawing. Check first that the receiving software imports AP242 annotations; geometry alone gains nothing.
AP242 is the newest protocol and the long-term direction of STEP. It can carry semantic PMI (product and manufacturing information): a position tolerance that knows which hole it belongs to, rather than a picture of a feature control frame. It also supports lightweight tessellated geometry, composites and richer assembly data.
The catch is that the benefit only appears when both ends support it. If the receiver strips the annotations on import, an AP242 file is just an AP214 file with a longer name.
When is AP203 still the right choice?
Choose AP203 when a customer, contract or legacy system names it. Some older aerospace and defence workflows were built around it and still require it. Otherwise it offers nothing AP214 lacks, and the first edition most tools write drops colours and layers.
AP203 is also the most conservative choice for very old software. If a recipient reports that a STEP file will not open at all, re-exporting as AP203 is a reasonable first test, though the cause is more often a surface model or a corrupt export than the protocol.
Which STEP version does PartWork.ai export?
STEP files exported from PartWork.ai Studio are AP214, with the schema AUTOMOTIVE_DESIGN in the header. They hold exact solid geometry with units declared, so they open at the right size in any CAD or CAM program and on instant-quote sites.
To check a STEP file before you send it, open it in the free online STEP viewer: it renders the solid in your browser and shows the part’s dimensions. If you have an old paper or PDF drawing and need a STEP file of the part, Drawing to STEP builds one from the drawing; see how to convert a PDF to CAD.
Frequently asked questions
Is AP214 better than AP203?
For most work, yes. AP214 carries the same solid geometry as AP203 and adds colours, layers and validation properties, and almost every CAD, CAM and quoting tool reads it. Pick AP203 only when a customer or contract asks for it by name.
Does the STEP version change the dimensions of my part?
No. All three protocols store the same exact B-rep solid, so the faces, edges and dimensions of a part are identical whichever one you export. The differences are in the extra data around the geometry: colours, layers, assembly metadata and annotations.
What is the FILE_SCHEMA line in a STEP file?
It is a line in the header near the top of every STEP file that names the protocol the file follows. CONFIG_CONTROL_DESIGN means AP203, AUTOMOTIVE_DESIGN means AP214, and a schema starting with AP242_MANAGED_MODEL_BASED means AP242. Open the file in any text editor to read it.
Should I export AP242 instead?
Export AP242 when the receiver needs annotations the software can read, such as tolerances and surface finish attached to faces, and their software supports AP242. For a plain part going to a shop or quoting site, AP214 is the safer default.
Do STEP files keep units?
Yes. Every STEP file declares its length unit, so a part exported in millimetres opens at the right size in software set to inches. This is true of AP203, AP214 and AP242 alike, and it is one reason STEP is safer to send than STL.
Want to see what is inside a STEP file?
Drop a .step or .stp file into the free viewer and inspect it in your browser, with nothing to install. It opens AP203, AP214 and AP242 files alike.