What Files to Send for 3D Printing: STL, 3MF, STEP, and Tolerance Checklist
Better file submissions do two things immediately: they speed up quoting and reduce revision loops. The right file type depends on whether the part is already ready to print or still needs modeling work, edits, or tolerance adjustments.
Which file type should you send?
| File type | Best use |
|---|---|
| 3MF | Best when you want a modern print-oriented file that preserves units and more model context |
| STL | Good for print-ready geometry when no major editing is expected |
| STEP or STP | Best when the part may need CAD edits, dimension changes, or feature cleanup |
| Images or PDF references | Useful supporting files for dimensions, fit notes, or replacement-part context |
When 3MF is better than STL
In modern print workflows, 3MF is often preferred over STL because it preserves more useful print context and avoids some of the ambiguity that comes with older mesh-only handoff habits. If your slicer or CAD workflow supports 3MF cleanly, it is often a strong default for print-ready submissions.
When STEP is better than either one
If the file may need dimensional edits, feature changes, or cleanup before printing, STEP is usually the more useful handoff. It gives the print service a better starting point for editable geometry. That matters for replacement parts, fit changes, and business jobs where the design may evolve between runs.
If you are ordering a replacement part rather than sending a finished CAD file, pair your files with the intake advice in our replacement-parts guide.
The tolerance checklist that prevents most delays
- Mark the critical dimensions and include units
- State the target fit: press-fit, slip-fit, snap-fit, or clearance
- Call out which surfaces are cosmetic and which are functional
- Describe the load direction or movement if the part is functional
- Note the environment: indoor, outdoor, warm area, moisture, or repeated handling
Submission gaps that slow projects down
- No unit scale provided
- No mating-part references for a fit-sensitive component
- No explanation of the part's real use-case
- No tolerance guidance even though the part needs to assemble with something else
A part can look simple and still be fit-sensitive. The small note that says "slight looseness is okay, but it cannot bind during install" is often more valuable than another screenshot.
What to send if you do not have a CAD file yet
You can still start a project with photos, rough dimensions, and reference images of where the part mounts. That is common on custom and repair jobs. What matters is making the context legible enough to scope the next step honestly.
FAQ
Is STL still acceptable?
Yes. STL is still widely usable for print-ready jobs, especially when the geometry does not need major editing.
Should I send 3MF if I have it?
Often yes, especially for print-ready submissions where preserving more print context is helpful.
What if I only have a broken part and photos?
That can still be enough to begin scoping. Add dimensions and mating-part references whenever possible.