Free tools / Hole sizes
Screw clearance & heat-set insert hole sizes for FDM
Starting points for CAD — not universal law. Printed holes usually come out small; print a diameter ladder on your machine before you lock a kit.
Screw clearance holes
Through diameters so a machine screw passes without cutting plastic. Use the tight end to locate; the loose end when stacking plates.
| Screw | CAD hole |
|---|---|
| M2 | 2.2–2.4 mm |
| M3 | 3.2–3.4 mm |
| M4 | 4.3–4.5 mm |
| M5 | 5.3–5.5 mm |
Heat-set insert pilots
Hole follows the insert outer geometry, not the M-size of the screw. Depth ≈ insert length + 1 mm. Always check your packet.
| Thread | Start hole | Note |
|---|---|---|
| M2 | ~3.2 mm | Check packet; series vary |
| M2.5 | ~4.0 mm | Common ruthex-style start |
| M3 | 4.0–4.2 mm | Datasheet often 4.0; many print 4.2 in CAD |
| M4 | ~5.6 mm | Confirm outer knurl |
| M5 | ~6.4 mm | Boss wall matters more |
Full walkthrough: How to design 3D printing tolerances in CAD.
Put the sizes in the manual
CAD gets the hole right for you. Builders still need the insert series and screw length on the step. That is what Slicebuild publishes.
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