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Coarse pitch: tap drill and clearance holes
| Thread | Pitch (mm) | Tap drill (mm) | Fine clearance (mm) | Medium clearance (mm) | Coarse clearance (mm) |
|---|---|---|---|---|---|
| M3 | 0.50 | 2.5 | 3.2 | 3.4 | 3.6 |
| M4 | 0.70 | 3.3 | 4.3 | 4.5 | 4.8 |
| M5 | 0.80 | 4.2 | 5.3 | 5.5 | 5.8 |
| M6 | 1.00 | 5.0 | 6.4 | 6.6 | 7.0 |
| M8 | 1.25 | 6.8 | 8.4 | 9.0 | 10.0 |
| M10 | 1.50 | 8.5 | 10.5 | 11.0 | 12.0 |
| M12 | 1.75 | 10.2 | 13.0 | 13.5 | 14.5 |
| M14 | 2.00 | 12.0 | 15.0 | 15.5 | 16.5 |
| M16 | 2.00 | 14.0 | 17.0 | 17.5 | 18.5 |
| M18 | 2.50 | 15.5 | 19.0 | 20.0 | 21.0 |
| M20 | 2.50 | 17.5 | 21.0 | 22.0 | 24.0 |
| M22 | 2.50 | 19.5 | 23.0 | 24.0 | 26.0 |
| M24 | 3.00 | 21.0 | 25.0 | 26.0 | 28.0 |
| M27 | 3.00 | 24.0 | 28.0 | 30.0 | 32.0 |
| M30 | 3.50 | 26.5 | 31.0 | 33.0 | 35.0 |
| M33 | 3.50 | 29.5 | 34.0 | 36.0 | 38.0 |
| M36 | 4.00 | 32.0 | 37.0 | 39.0 | 42.0 |
The tap drill gives a thread with about 75 % engagement, suitable for steel and aluminium. Clearance holes (ISO 273) are for bolts that pass through a part without a thread: “medium” is the usual choice, “fine” for precise positioning, “coarse” for assembly with wide tolerances.
Fine pitch: tap drill
| Fine-pitch thread | Tap drill (mm) |
|---|---|
| M8×1 | 7.0 |
| M10×1 | 9.0 |
| M10×1.25 | 8.8 |
| M12×1.25 | 10.8 |
| M12×1.5 | 10.5 |
| M14×1.5 | 12.5 |
| M16×1.5 | 14.5 |
| M18×1.5 | 16.5 |
| M20×1.5 | 18.5 |
| M20×2 | 18.0 |
| M22×1.5 | 20.5 |
| M24×1.5 | 22.5 |
| M24×2 | 22.0 |
| M27×2 | 25.0 |
| M30×1.5 | 28.5 |
| M30×2 | 28.0 |
| M36×3 | 33.0 |
For hard materials or stainless steel, tap manufacturers sometimes recommend a slightly larger drill (lower thread engagement). Follow the data sheet of the tap you use.
Frequently asked questions
Which drill do I use for M8?
A 6.8 mm drill for M8 with coarse pitch (1.25 mm). For M8×1 (fine pitch) use 7 mm.
Which drill do I use for M10 and M12?
M10 (pitch 1.5): 8.5 mm. M12 (pitch 1.75): 10.2 mm. For M12×1.5 (fine pitch): 10.5 mm.
What is the difference between coarse and fine pitch?
Fine pitch has more threads per length: it holds better against vibration and allows more precise adjustment, but is more easily damaged. Coarse pitch is the standard, used unless stated otherwise.
What drill lets an M8 bolt pass through a part?
Medium clearance hole of 9 mm (fine 8.4 mm, coarse 10 mm), per ISO 273.