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What is STEP AP242?

STEP (ISO 10303) is the international standard for exchanging product data between CAD systems. It is organized into application protocols, or APs, each tailored to a set of industrial needs. AP242, titled "Managed model-based 3D engineering", is the most recent and most complete protocol for mechanical design data.

Beyond B-rep geometry and assemblies, AP242 can carry tessellated geometry for lightweight visualization and both graphical and semantic product manufacturing information (PMI), such as dimensions, geometric tolerances and datums linked to the faces they apply to. This makes it the reference neutral format for model-based definition (MBD), where the 3D model replaces the 2D drawing as the authoritative source.


AP203 vs. AP214 vs. AP242

ProtocolOriginMain content
AP203Aerospace and defense designConfiguration-controlled 3D design: geometry and assemblies. The first edition does not support colors or layers; edition 2 added them
AP214Automotive design3D geometry with colors, layers and assembly presentation
AP242Merger of AP203 and AP214 (2014)Geometry, assemblies, tessellated geometry, graphical and semantic PMI for model-based definition

AP242 editions

EditionYearFocus
Edition 12014First release, merging AP203 and AP214 and adding model-based 3D engineering
Edition 22020Extension to electrical design, with enhancements for PDM, 3D geometry, 3D PMI, composites and mechanical design
Edition 32022Corrective maintenance edition

What Is STEP AP242 Used For? Applications and Industry Use Cases

AP242 is used wherever companies exchange 3D models across CAD systems and suppliers while keeping manufacturing information intact: aerospace, defense, automotive and industrial machinery in particular. It supports model-based definition, long-term archiving of engineering data and digital thread initiatives that connect design to manufacturing and inspection.

For software developers, AP242 support allows CAM, inspection, metrology and analysis applications to receive dimensions, tolerances and datums that are directly linked to geometry, and to use them without manual re-entry. It also lets applications exchange lightweight, tessellated models with graphical PMI for visualization.


Challenges or Common Pitfalls

Not every STEP file is an AP242 file. Many CAD systems still export AP203 or AP214 by default, and those protocols cannot carry semantic PMI or full tessellated data. Choosing the right protocol, and checking what the sending application really writes, is essential in MBD workflows.

PMI fidelity is another challenge. Graphical PMI shows annotations as text and lines for humans, while semantic PMI describes tolerances and datums in a form that software can interpret. Translators vary in how completely they read, link and write both kinds, and some symbols or assembly-level annotations may not be supported everywhere.

Finally, the standard keeps evolving through new editions, so it is worth confirming which edition a given tool reads and writes.


How Spatial Helps

Our 3D InterOp SDK reads and writes AP203, AP214 and AP242 files with the .step, .stp and .stpx extensions, including assembly structure, B-rep geometry, visualization geometry, graphical PMI and attributes, for CGM Modeler, 3D ACIS Modeler and Parasolid. AP214 is the default write version, and files are written as AP242 automatically when they include visualization data or semantic PMI.

With the STEP AP242 Reader/Writer add-on, aligned with ISO 10303-242:2022 (Edition 3), 3D InterOp handles semantic PMI: views and annotations, datum features and targets, GD&T, dimensions and notes. Applications can author part-level semantic PMI and export it, and since Release 2026 1.0, semantic PMI can be linked to its graphical representation. On export, AP242 files can contain tessellated geometry only, tessellated geometry with tessellated PMI, B-rep with tessellated PMI, or B-rep with tessellated geometry.

For large models, multi-process import speeds up STEP loading for all three modelers, and since Release 2026 1.0 the Hidden Body Removal capability of our Data Prep technology works with STEP assemblies in UConnect workflows.

Dassault Systèmes

Siemens

Autodesk

Standards

Other

  • Pro/E / Creo
  • Rhino
  • MicroStation DGN
  • AVEVA
  • Smart3D

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