Published 2026-10-29 · 2 min read
3D printing tolerances for parts that fit together
You draw a 10 mm shaft and a 10 mm hole, print them, and the shaft will not go in. It is not your printer's fault: on screen two parts of the same size touch perfectly; in melted plastic they do not. You need clearance — and how much depends on what the joint should do.
How much clearance
For a well-tuned FDM printer with a 0.4 mm nozzle, these are good starting values (per side):
| Joint | Clearance per side | Example: 10 mm shaft |
|---|---|---|
| Press fit, stays in | 0.05–0.1 mm | 10.1–10.2 mm hole |
| Tight, comes out with effort | 0.15 mm | 10.3 mm hole |
| Sliding (lids, drawers) | 0.2–0.3 mm | 10.4–10.6 mm hole |
| Free running (hinges) | 0.4–0.5 mm | 10.8–11 mm hole |
Why holes print small
- The slicer approximates circles with straight segments, and the segments cut inwards. Export at high resolution.
- Plastic shrinks a little as it cools: PLA around 0.3%, ABS and ASA up to 0.7–0.8%.
- The first layer is squashed onto the bed and spreads (“elephant's foot”) by 0.1–0.2 mm. A 0.5 mm chamfer on the bottom edge fixes it.
- Horizontal holes come out oval. Make them teardrop-shaped or print the part in another orientation.
Screws and nuts
- Clearance hole for M3: 3.3–3.4 mm. For M4: 4.4 mm.
- Hole for a self-tapping M3 screw: 2.6–2.8 mm.
- Hex pocket for an M3 nut: 5.7 mm across flats, plus 0.2 clearance.
- Heat-set threaded inserts: the size the maker specifies, usually ~4.0–4.2 mm for M3.
Run a 10-minute test
Every printer and every filament is a little different. Print a shaft and a plate with five holes: +0.1, +0.2, +0.3, +0.4, +0.5 mm. Note which one fits the way you want and use that value on every part.
In GrafitGo's mechanical editor the plate takes two minutes: a box, five cylinders of different diameters, the difference operation, STL export. The print check confirms the part is closed and fits the bed.
Can I fix tolerance in the slicer instead of the model?
Partly: most slicers have hole compensation and first-layer compensation. Good for fine-tuning, but put the base clearance in the model.
Does material matter?
Yes. PETG oozes more and needs a bit more clearance than PLA; ABS shrinks more as it cools.
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