Tap drill and clearance hole chart
The tap drill is the hole you cut threads into. The clearance hole is the hole the screw passes straight through. Getting these wrong is the number one cause of stripped threads.
| Size | Pitch | Tap drill | Clearance (close) | Clearance (normal) |
|---|---|---|---|---|
| M1.2 | 0.25 mm | 0.95 mm | 1.3 mm | 1.4 mm |
| M1.4 | 0.3 mm | 1.1 mm | 1.5 mm | 1.6 mm |
| M1.6 | 0.35 mm (fine 0.2) | 1.25 mm / 1.4 fine | 1.7 mm | 1.8 mm |
| M2 | 0.4 mm (fine 0.25) | 1.6 mm / 1.75 fine | 2.2 mm | 2.4 mm |
| M2.5 | 0.45 mm (fine 0.35) | 2.05 mm / 2.15 fine | 2.7 mm | 2.9 mm |
| M3 | 0.5 mm (fine 0.35) | 2.5 mm / 2.65 fine | 3.2 mm | 3.4 mm |
| M4 | 0.7 mm (fine 0.5) | 3.3 mm / 3.5 fine | 4.3 mm | 4.5 mm |
| M5 | 0.8 mm (fine 0.5) | 4.2 mm / 4.5 fine | 5.3 mm | 5.5 mm |
| M6 | 1 mm (fine 0.75) | 5 mm / 5.25 fine | 6.4 mm | 6.6 mm |
Tapping plastic and 3D prints
Plastic holds better with a slightly larger hole than metal — aim for about 0.1 mm above the metal tap drill and use a thread-forming screw rather than cutting threads. For 3D prints, a heat-set brass insert is far stronger than threads cut into the plastic itself.
Self-tapping and thread-forming sizes →Rules of thumb
- Tap drill ≈ screw diameter minus the pitch. M3 with a 0.5 mm pitch → 2.5 mm.
- Thread depth of about 1.5× the diameter is plenty in steel, 2× in aluminium.
- Back the tap out a half turn every full turn to break the chip, especially under M3.
- Use cutting fluid. Taps under 2 mm snap very easily and are miserable to remove.
Gear for this job
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Metric tap and die set
For cutting or chasing threads
Small tap drill bit set
Matching tap-drill sizes
Cutting fluid
Small taps snap without it