STEP AP242

The current STEP application protocol, built to carry a model-based product definition, geometry plus PMI, rather than geometry alone.

Definition

What is STEP AP242?

STEP AP242, formally ISO 10303-242, is the application protocol within the STEP family built for managed, model-based 3D engineering. Its scope covers products of automotive, aerospace and other mechanical manufacturers and their suppliers, including parts, assemblies, tools and raw materials, together with product manufacturing information, process-plan information and interfaces with version management.1

AP242 is the result of merging aerospace's AP203 (configuration-controlled 3D design) and automotive's AP214 (core data for automotive mechanical design processes) into a single protocol, first published in 2014 and since extended through further editions, most recently Edition 4 in 2025.1

Why AP242 exists: model-based definition

Before AP242, a 3D model and its tolerancing information typically lived in two places: the CAD model and a separate 2D drawing. Manufacturing and inspection then had to reconcile the two by hand. AP242 was designed to support Model-Based Definition (MBD): tolerances, datums and other Product and Manufacturing Information attached directly to model geometry as machine-readable data, not only as a visual annotation for a person to read.2

That distinction matters for manufacturing software specifically. A tolerance shown only as a picture on a drawing has to be re-typed or manually linked to the geometry it controls before software can reason about it. A tolerance carried as semantic PMI in an AP242 file is already structured data tied to a specific face or edge.

What this does and does not solve

AP242 being capable of carrying PMI does not mean every AP242 file does. Whether PMI actually travels with a given file depends on the authoring CAD system, its export settings and the modelling discipline used to create the part. NIST's own applied research on standards-based interoperability was built around exactly this handoff problem: getting a model-based product definition to survive intact from design through manufacturing and quality inspection.3 Recent NIST work continues to address the practical migration of PMI models to a common, more usable core.4

For manufacturing reasoning, the practical consequence is that manufacturing feature recognition and manufacturability checks still need to handle both cases: a file where PMI is genuinely present as structured data, and the still-common case where it is not, and the drawing remains the source of truth.

Frequently asked questions

Is AP242 the same thing as STEP?

AP242 is one application protocol within the STEP (ISO 10303) family: the current, actively developed one for model-based 3D engineering.

Does an AP242 file always include PMI?

No. The protocol supports carrying PMI; whether a specific export includes it depends on the authoring CAD system and how the file was generated.

What replaced AP203 and AP214?

AP242 merged and extended both, adding support for a fuller model-based product definition.

Notes & references

  1. International Organization for Standardization (2025). ISO 10303-242:2025, Industrial automation systems and integration — Product data representation and exchange — Part 242: Application protocol: Managed model-based 3D engineering (Edition 4). ISO. https://www.iso.org/standard/84300.html Defines the current scope and content of STEP AP242.
  2. Barnard Feeney, A., Frechette, S. P. & Srinivasan, V. (2015). A Portrait of an ISO STEP Tolerancing Standard as an Enabler of Smart Manufacturing Systems. Journal of Computing and Information Science in Engineering, 15(2), 021001. https://doi.org/10.1115/1.4029050 Describes how AP242's tolerancing capabilities are intended to enable smart, model-based manufacturing systems.
  3. Fischer, K., Rosche, P., Trainer, A., Barnard Feeney, A. & Hedberg, T. (2015). Investigating the Impact of Standards-Based Interoperability for Design to Manufacturing and Quality in the Supply Chain. NIST GCR 15-1009. https://doi.org/10.6028/NIST.GCR.15-1009 NIST-funded research on getting a model-based product definition to survive the handoff from design to manufacturing and inspection.
  4. Barnard Feeney, A. & Thurman, T. (2023). On Migrating ISO 10303 PMI Models to a Common Core. NIST AMS 100-51. https://doi.org/10.6028/NIST.AMS.100-51 Discusses practical migration of ISO 10303 PMI models toward a common, more usable core.