Tools · 4 min read
CAD File Formats Explained: STEP, IGES, STL, OBJ, and DXF
Sharing a 3D model often fails not because of the model but because of the format. CAD formats fall into a few families, and each is right for a different job.
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Exact solids: STEP and IGES
STEP (.step, .stp) stores precise mathematical surfaces and solids. It is the standard for exchanging parts between different CAD programs and for CNC machining, because holes stay perfect circles. IGES is its older predecessor; it is still used but mostly carries surfaces rather than solids.
Meshes: STL and OBJ
STL describes a surface as thousands of triangles, with no units, colours, or design history. It is the classic 3D-printing format. OBJ is also a mesh but can carry colours and textures, making it common for visualisation and games. Once a part is a mesh, curves become flat facets and it is hard to edit precisely.
2D drawings: DXF
DXF is AutoCAD's exchange format for 2D drawings — lines, arcs, and text. It is what laser cutters, plasma cutters, and CNC routers typically expect for flat parts.
Which format to send
For 3D printing, send STL (or 3MF). For machining or a colleague with different CAD software, send STEP. For laser cutting, send DXF. Always confirm the units — an STL has none, so a part in millimetres can arrive 25 times too big if read as inches.