File formats

open / import read a file into the scene; save / export write it. The format is chosen by extension.

Format	Import	Export	Notes
.serp	✓	✓	Native: JSON scene + embedded binary BREP, thumbnail and metadata
.step / .stp	✓	✓	Exact BREP exchange via OpenCASCADE
.3dm	✓	✓	Rhino: exact NURBS curves both ways; breps import as trimmed NURBS faces, export as meshes (use STEP for exact surfaces); layers with visibility/lock and hidden objects preserved; writes Rhino 5–8
.obj	✓	✓	Tessellated mesh with .mtl colours
.fbx	✓	✓	Autodesk FBX (binary) — tessellated meshes; imports/exports cleanly to Blender, Maya, Unreal, Unity
.stl	✓	✓	3D printing — watertight binary (or ASCII) STL for slicers, with draft→ultra mesh-quality presets on export
.3mf		✓	3D printing — modern container with real units, colour and multi-part; preferred by Bambu Studio / PrusaSlicer / Cura
.dxf	✓	✓	Curves/meshes with layers; layout sheets export at paper scale
.svg	✓	✓	Paths import as curves (béziers exact); layouts export as vector SVG
.glb		✓	Binary glTF with materials (Unreal / Blender / web)
.usda / .usd		✓	USD for virtual-production pipelines

Notes

• Exact vs. mesh. .serp and .step carry exact geometry both ways; .3dm is exact for curves but writes surfaces and solids as meshes — for an exact round trip through Rhino, export STEP and import it there. .obj, .fbx, .stl, .3mf, .glb and .usd are tessellated meshes — the display deflection (or STL quality preset) sets how fine.
• Layouts. exportpdf and exportsvg write drawing sheets, honouring linetypes and hidden-line detail modes.
• Coordinate system. Serpentine3D is Z-up. FBX export declares the Z-up axis system so orientation survives into Blender and others.
• Headless. Every format works from a script — doc.export("part.step") or serp3d-batch (see Script & automate).