Short answer
Send an STL. It is what the quote tool reads and what printers ultimately use. Keep a STEP file yourself for future edits, and send that too if the part needs modifying before printing.
Two different kinds of 3D file
Almost every format falls into one of two camps, and the difference explains everything else.
Mesh formats (STL, OBJ, 3MF) describe a surface as thousands of flat triangles. A curve is not a curve; it is many short straight edges approximating one. Simple, universal, and impossible to edit meaningfully afterwards.
Solid model formats (STEP, IGES) describe shapes mathematically — a cylinder is stored as a cylinder with a radius. They can be edited precisely in CAD, and they are much larger and more complex to process.
STL: the printing standard
STL is what every slicer expects, and it is what our quote tool reads directly in your browser to work out the price. It carries geometry and nothing else — no units, no colour, no material.
The unit issue is the one that bites. Because an STL has no units, a model exported in inches arrives looking 25 times too small. If your part appears absurdly sized in the quote tool, that is almost always why.
The other STL setting worth knowing is resolution. Export too coarse and curved surfaces show visible facets; export too fine and you get a 400 MB file that takes a minute to load and prints identically. Somewhere in the middle — where curves look smooth on screen — is right.
STEP: better for editing, not for printing
A STEP file keeps true geometry, so it can be modified accurately: a hole moved, a wall thickened, a feature added. If a part needs changing before it is printed, STEP saves redrawing it from scratch.
It cannot be printed directly — it has to be converted to a mesh first — but that conversion is trivial at our end. The real reason to care is that you should keep the STEP for yourself. An STL is effectively a one-way export.
3MF: the modern format nobody uses yet
3MF fixes STL's shortcomings: it stores units, colours, multiple parts and even print settings in one compressed file. It is genuinely better, and support is growing steadily. It is simply not yet universal, which is why STL remains the default. We can accept 3MF by email.
OBJ, and why we rarely see it
OBJ comes from the graphics and animation world and carries textures and colours alongside geometry. For a single-colour functional part that information is irrelevant, and OBJ files often arrive with scale and orientation quirks. It works, but STL is less trouble.
Exporting cleanly
- Fusion 360 — right-click the body, Save As Mesh, STL, refinement Medium or High
- SolidWorks — Save As, STL, then Options to set resolution; check units are millimetres
- FreeCAD — select the body, File then Export, choose STL
- Blender — apply modifiers first, then File, Export, STL, with Selection Only ticked
- TinkerCAD — Export, then .STL; it is millimetres by default
Whatever the package, open the exported file in a viewer before sending it. Thirty seconds of checking catches most problems.
Common questions
Which file format should I send?
STEP if you have it, otherwise STL. STEP keeps true curves and real units, so we can adjust a clearance properly instead of editing a triangle mesh.
What is wrong with STL files?
Nothing fatal, but STL stores only triangles and carries no units. Curves become facets and the receiving software has to guess whether you meant millimetres.
Is 3MF better than STL?
Yes, modestly. 3MF carries units, colour and multiple parts in one file, so there is less to go wrong. It is still a mesh, not true geometry.
Can you work from a STEP file directly?
Yes, and we prefer it. With STEP we can enlarge a hole or add clearance cleanly, which is difficult and lossy on a mesh.
Does the format affect the price?
Not directly, but a STEP file sometimes saves us repair or remodelling time, and that does show up in the quote on anything we have to adjust.
What if I only have a photo or a drawing?
That is fine, we work from those regularly. Send what you have with a ruler in shot and we will model the part before printing it.
What this means when you order
If all you have is a STEP, 3MF or OBJ, email it over rather than trying to force it through the quote tool — we will convert it and send a price back.
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Published 7 September 2026 · last reviewed 5 October 2026.