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ISO 10303 (STEP)

STEP or ISO 10303 or “Standard for the Exchange of Product model data” is a newer standard designed for exchange of product manufacturing data. The goal of the STEP exchange format was to describe a product and its manufacturing lifecycle independent of any specific software or hardware system.

STEP is a plain text file format. Each STEP file has following sections:

  • Header. Contains file name, description and schema. Could contain other optional properties like section language, section context and others.
  • Anchor. Defines external labels for instances of data in the exchange structure so they can be referenced externally.
  • Reference. Defines external references to data entities in other files specified by their URI.
  • Data. Contains actual content of the file. Entities in data section should match either EXPRESS schema or customer user schema.
  • Signature. Section with a signature of a file which permits verification that data in STEP file was not corrupted.

STEP specification allows multiple files in one CAD exchange. To store multiple files PKZIP 2.04g compression could be used. In case of multiple file exchange, compressed STEP package should contain ISO10303.p21 file. ISO10303.p21 is a root file which should contain at least a header section of a STEP file. Also STEP multiple file exchange allows storing CAD exchange files in a single directory with no compression.

STEP uses EXPRESS data modeling language. EXPRESS is a full procedural programming language with support for object-oriented concepts with a very powerful and general inheritance.

STEP is the most popular CAD data exchange format and replaced IGES as a standard for CAD data exchange used by commercial and government organization. It is actively being developed by technical committee TC 184.

STEP format doesn’t require a license to be used and 3rd party developers can use the format in their applications. A good place to start would be STEP Tools Software which contains multiple open-source projects based on STEP.

STEP uses STP, STEP and P21 file extensions to store exchange data.

CAD Exchange Formats
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Extension Details
AutoCAD Drawing File Format
MIME Type
  • application/acad
  • application/x-acad
  • application/autocad_dwg
  • image/x-dwg
  • application/dwg
  • application/x-dwg
  • application/x-autocad
  • image/vnd.dwg
  • drawing/dwg
Opens with
  • Autodesk AutoCAD
  • DWG TrueView
  • Autodesk Online Viewer