DATA FORMATSCAD/CAM data formats

What arrives depends on the format you use, whether you receive a 3D model from a customer or hand it from your own CAD to CAM. A common format for exchanging data between different CAD and CAM systems is called a neutral format (intermediate file); STEP and IGES are examples^[1][2][3].

≡What each format carries

Format	Geometry	Tolerances, notes	Color, layers	Units	Modeling history
STEP AP242Neutral format	○Solids, surfaces, wireframe, mesh^[4][5]	○Dimensional tolerances, geometric tolerances, PMI (semantic / graphic)^[4][5]	―	―	△History is lost (can carry machining features)^[3][4]
STEP AP203/AP214Neutral format	○Geometry (B-rep solids, etc.)^[4][1]	―	―	―	×History is lost^[3]
IGESNeutral format (legacy)	○Geometry (geometry and topology), drawing entities^[2][3]	△Notes carry over, but tolerances written as text lose their numeric meaning^[2][3]	―	―	×History is lost^[3]
Parasolid (XT)Kernel format	○B-rep (solids, surfaces, mesh)^[6]	―	―	―	―
ACISKernel format	○B-rep^[7]	―	―	―	―
DXF2D drawings	○Mainly 2D drawings (some 3D); more than 60 entity types^[8]	―	○Layers and blocks carry over^[8]	―	―
DWGAutoCAD native	△AutoCAD drawings (official specification not published)^[9]	―	―	―	―
STLMesh	△Triangle mesh shape only^[10]	―	×No color standard^[10]	×No units^[10]	―
3MFMesh (for additive manufacturing)	○Mesh; multiple objects in one file^[11]	―	○Color and materials (extension specification)^[11]	○Has coordinates and units^[11]	―
NativeSpecific to each CAD system	○Geometry^[3][12]	―	―	―	○Carries history, features, and constraints^[3][12]

○ = carried over, △ = partial or conditional, × = not carried over, – = not checked in the sources used here. Results also vary with the format version and the settings of the exporting CAD.

STEP (ISO 10303)

Neutral format (international standard)Extensions: .stp, .step, .p21^[1]

An international standard for exchanging product data between CAD, CAM, and CAE. The file is text in the ISO 10303-21 syntax. An “application protocol (AP)” is defined for each purpose, and the contents differ depending on which AP was used to write the file.^[1][4]
What it carries:Geometry (B-rep solids, etc.), plus product structure, tolerances, and notes depending on the AP^[4][1]
Background:IGES served as the foundation on which the international standard was developedOne source / reference^[2]

Application protocols (AP)

AP203 (Configuration controlled design)

An AP used mainly in aerospace and defense. Published in 1994, revised in 2011.One source / reference^[1]

AP214 (Core data for automotive mechanical design processes)

An AP used mainly in the automotive supply chain. Maintained by ProSTEP iViP and SASIG.One source / reference^[1]

AP242 (Managed model-based 3D engineering)

An AP that merges and extends AP203 and AP214. Edition 1 was published in 2014, editions 2 and 3 in 2020; the current ISO version is ISO 10303-242:2025.^[1][13][4]
What it carries:Multiple geometry representations (solids, surfaces, wireframe, mesh/tessellation), dimensional and geometric tolerances, 3D models with annotations (PMI), machining features, surface conditions, assemblies, kinematics, composites, and more^[4][5]
PMI:PMI comes in two kinds: “semantic PMI” (tolerance data whose meaning software can read) and “graphic PMI” (annotation for appearance only, with no meaning attached). The receiver needs semantic PMI to use tolerances automatically.One source / reference^[5]

PMI (product and manufacturing information) is information such as dimensions, tolerances, and datums attached to a 3D model^[5][4]. For how tolerances are written on drawings, see Draftingpage.

IGES (Initial Graphics Exchange Specification)

Neutral format (legacy)

A specification for exchanging geometry, graphics, and notes between CAD systems; the first edition came out in 1980 under the US NBS (now NIST). It became an ANSI standard in 1981 and was adopted as a national standard in Japan and elsewhere. It became the foundation of STEP.^[2][3]
What it carries:Geometry (geometry and topology), graphics data, notes^[2][3]
File:Comes as text (fixed-length 80-character lines) or binaryOne source / reference^[3]

Parasolid (XT format)

Kernel format

Siemens' 3D geometric modeling kernel. It handles solids, surfaces, and mesh as B-rep (boundary representation), and is used in the products of more than 200 software companies. The standard file format is Parasolid XT.One source / reference^[6]
What it carries (per Siemens):Geometry (B-rep). Software that uses the same kernel is less prone to conversion errorsOne source / reference^[6]

ACIS

Kernel format

A 3D geometric modeling kernel from Spatial (Dassault Systèmes group). It represents shapes as B-rep and has the ACIS file format.One source / reference^[7]

DXF

2D drawing exchange formatExtension: .dxf^[8]

A format defined by Autodesk for exchanging the contents of AutoCAD drawings with other software. Mainly 2D drawings, with some 3D support. Comes as text (pairs of group codes and values) or binary.One source / reference^[8]
What it carries:More than 60 entity types, layers, blocksOne source / reference^[8]
Note:The specification changes with each AutoCAD release, and some entities are poorly documented.One source / reference^[8]

DWG

Native format (AutoCAD)Extension: .dwg^[9]

AutoCAD's own native format (binary). Autodesk does not publish an official specification, and the specification reverse-engineered by the Open Design Alliance is the most detailed. The version changes every 2–3 years.One source / reference^[9]

STL

Mesh formatExtension: .stl^[10]

A format that represents a solid's surface as a collection of triangular facets (vertex coordinates and outward normals). Created in 1988 by 3D Systems for stereolithography. Comes as text or binary.One source / reference^[10]
What it carries:Triangle mesh shape only. No unit information and no color standardOne source / reference^[10]
Use in CAM:Curved surfaces become faceted triangles, so it is not suited as source data for precision finishing. When using it in CAM, watch the fineness (triangle size).One source / reference^[10]

3MF (3D Manufacturing Format)

Mesh format (for additive manufacturing)Extension: .3mf^[11]

A format with XML inside a ZIP, maintained by the 3MF Consortium (founded in 2015).One source / reference^[11]
What it carries:Coordinates and units, color and materials (extension specification), multiple objects in one fileOne source / reference^[11]

Native format (specific to each CAD)

Native format

Each CAD system's own format. It carries modeling history, features, constraints, and so on, but converting to a neutral format usually drops those and leaves only the shape.^[3][12]

With CAM built into the CAD, or CAM embedded in the same CAD, you can skip conversion (see the software list, “CAD integration”)

⏱From IGES to STEP AP242

Gray = IGES, green = STEP. Spacing is not proportional to years.

!Problems that occur in exchange

Faces do not close into a solid (missing faces, gaps):When STEP or IGES is imported, faces may not join automatically and gaps remain. Faces that failed to join are left as separate faces, so re-stitch them by changing the gap tolerance, or repair the faces.One source / reference^[14]
Quality requirements:Quality items and recommended values for exchange are defined in Japan by the JAMA/JAPIA PDQ guidelines (shape, drawings, CAE mesh) and internationally by ISO 10303-59 on product shape data quality.^[15][16]
Unit mismatch (mm vs. inch):STL carries no units, so the receiver must decide whether to read it as mm or inch. Some software sets the CAM internal unit and the NC program output unit (G20/G21) separately, and mixing them up throws dimensions off by a large amount.^[10][17]
Tolerance and note meaning is lost:Tolerances written as text on a drawing lose their numeric meaning on conversion. Even 3D notes, if they are appearance-only graphic PMI, cannot be read as tolerances by the receiving software.^[3][5]
Feature and shape meaning is lost:Neutral formats drop the modeling history. If a cylindrical hole arrives as a NURBS surface, CAM cannot recognize it as a “hole,” and a person has to decide between a drill and an end mill. Offset surface information is also lost.One source / reference^[3]
Color and layers do not carry over:STL has no color standard and two incompatible ways of writing it. To carry color and materials, use the 3MF extension specification. Drawing layers can be passed in DXF.One source / reference^[10][11][8]
Cannot open due to version differences:DWG changes format with each AutoCAD version and has no official specification, so it may not open if the other party's software does not support the newer version.One source / reference^[9]

Unit commands:G20,G21(G/M code dictionary). For how to check after importing, see Common mistakes.

Other CAD/CAM pages

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📚Sources

The format descriptions are based on Library of Congress format descriptions, public ISO and NIST pages, the developers of each kernel, and university materials.