.STEP
Standard for the Exchange of Product Model Data
Introduction
STEP is the ISO 10303 standard for exchanging product data between CAD systems. A STEP file carries exact solid geometry, as boundary surfaces rather than triangles, along with assemblies, units and, depending on the application protocol, colours, tolerances and product information. It is the most common neutral format for moving 3D models between different CAD programs.
The file says which application protocol it follows, such as AP203, AP214 or AP242.
Files use the extension .step or .stp.
Software
- FreeCAD (Windows, macOS, Linux)
- Autodesk Fusion (Windows, macOS)
- Autodesk Inventor (Windows)
- SolidWorks (Windows)
- Onshape (web browsers)
- Rhino (Windows, macOS)
Structure
The common encoding, ISO 10303-21, is plain text. It opens with
ISO-10303-21;, then a HEADER section naming the file, its
author, the program that wrote it and the schema it follows. The DATA
section lists numbered entity instances, one per statement, each referring to others
by number. The file closes with END-ISO-10303-21;.
ISO-10303-21;
HEADER;
FILE_DESCRIPTION(('a bracket'),'2;1');
FILE_NAME('bracket.step','2026-01-01T00:00:00',(''),(''),'','','');
FILE_SCHEMA(('AUTOMOTIVE_DESIGN'));
ENDSEC;
DATA;
#1=CARTESIAN_POINT('',(0.,0.,0.));
#2=DIRECTION('',(0.,0.,1.));
#3=AXIS2_PLACEMENT_3D('',#1,#2,$);
ENDSEC;
END-ISO-10303-21;