Every engineer eventually sends the wrong file. The architect gets a STEP file when they asked for a floor plan. The CNC shop receives a DWG full of proxy objects their software can't read. Five minutes of format knowledge prevents all of it.
DWG — the native format
DWG is Autodesk's proprietary binary format and the de facto standard of 2D drafting. It's compact, carries every AutoCAD feature (dynamic blocks, constraint systems, custom objects), and every serious CAD tool reads it.
The catch: it's versioned internally. A file saved in AutoCAD 2024 (AC1032 internally) won't open in AutoCAD 2013 without down-conversion, and features added in newer versions can be silently dropped. You can identify the version from the file itself — the first six bytes of any DWG are an ASCII code like AC1032 — something our free DWG version checker reads locally in your browser in milliseconds.
Send DWG when: your recipient works in an AutoCAD-compatible tool and you control the version they save to.
DXF — the open exchange format
DXF is Autodesk's documented interchange format — the spec is public, which is why every CNC controller, laser cutter, plotter, and viewing tool on earth understands it. It comes in ASCII (huge but diff-able) and binary (compact) flavors.
What it won't do: carry the full richness of modern DWG (no dynamic blocks, limited constraint data), and 3D support is rudimentary.
Send DXF when: feeding a CNC machine, laser cutter, or any downstream tool that isn't a full CAD package. For 2D profiles and flat patterns it's the lingua franca.
STEP — the neutral 3D standard
STEP (ISO 10303) is the international standard for exchanging 3D solids between different CAD systems. It carries exact B-rep geometry — not meshes — so a part modeled in SolidWorks opens in NX, Creo, or CATIA as a real, editable solid.
Know your APs: AP203 is the classic, AP214 adds colors and materials, AP242 is the current generation with model-based definition (PMI) support. And expect feature trees to vanish: STEP transfers geometry, not history. The recipient gets a dumb solid they can measure and modify, not re-parameterize.
Send STEP when: crossing company or CAD-platform boundaries in 3D. It is the professional default.
IGES — the veteran
IGES predates STEP and still shows up in aerospace and automotive supply chains. It handles surfaces well but solids poorly, and tolerance mismatches between systems produce the infamous "sewed surface" repairs. Treat it as legacy: receive it when you must, send STEP instead when you have the choice.
STL / 3MF — the mesh world
STL stores nothing but triangles — no units, no colors (in the classic form), no precision semantics. It rules 3D printing because slicers don't need more. 3MF is the modern replacement carrying units, materials, and structure. Never use STL as a CAD deliverable; it's a manufacturing instruction, not a design document.
The five-second decision
- 2D drawing to an AutoCAD-compatible user → DWG
- 2D profile to a machine → DXF
- 3D model across companies or CAD systems → STEP (AP242 if you can)
- Legacy aerospace supplier → IGES (grudgingly)
- 3D printer → STL or 3MF
And when in doubt, ask the recipient what they're opening it with — then check tool compatibility before you send. We track file format support for 170+ CAD tools at CADGuide.tools/file-formats, free as always.
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