M10 tap drill size
The tap drill for M10×1.5 is 8.5 mm. That’s the standard chart size and gives about 77% of full thread.
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Tap drill by thread percentage
75% is the usual workshop figure. Less thread is easier to tap; more adds little strength.
| Thread % | Ideal drill | Nearest metric drill | Nearest imperial drill |
|---|---|---|---|
| 60% | 8.831 mm 0.3477" | 8.8 mm (62%) | letter S 0.3480" (60%) |
| 65% | 8.733 mm 0.3438" | 8.7 mm (67%) | 11/32" 0.3438" (65%) |
| 70% | 8.636 mm 0.3400" | 8.6 mm (72%) | letter R 0.3390" (71%) |
| 75% | 8.539 mm 0.3362" | 8.5 mm (77%) | letter R 0.3390" (71%) |
| 80% | 8.441 mm 0.3323" | 8.4 mm (82%) | letter Q 0.3320" (80%) |
About this size
ISO metric coarse is the default thread for general engineering in the UK and Europe. If a drawing just says “M10”, it means the coarse pitch.
- For stainless steel, duplex and other tough materials, go to about 65% thread: a 8.7 mm drill gives 67%. For mild steel, brass and cast iron the 8.5 mm is fine.
- For a blind hole with 1.5 × D thread engagement (15 mm), drill about 21 mm deep. That leaves room for the 3–4 tapered lead threads on a second or plug tap. In steel, 1 × D engagement is usually enough; in aluminium or cast iron allow 1.5–2 × D.
Clearance holes for M10
| Fit | Drill |
|---|---|
| Close | 10.5 mm (0.413") |
| Medium (normal) | 11 mm (0.433") |
| Free (loose) | 12 mm (0.472") |
Fine, medium and coarse series from ISO 273. Medium suits most jobs; use fine where parts must locate closely and coarse for quick assembly or coated bolts.
M10 thread data
| Designation | M10×1.5 |
|---|---|
| Standard | ISO 68-1 basic profile, ISO 261/262 series |
| Pitch | 1.5 mm pitch (16.9 TPI equivalent) |
| Thread angle | 60° |
| Major diameter | 10 mm (0.394") |
| Pitch (effective) diameter | 9.026 mm (0.355") |
| Minor diameter, external | 8.16 mm (0.321") |
| Minor diameter, internal | 8.376 mm (0.330") |
| Thread depth (internal) | 0.812 mm |
Basic sizes. Real screws are slightly under and real nuts slightly over these values because of tolerance classes.
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Nearest alternatives
If you don’t have the right drill, these give:
- 8.4 mm drill → about 82% thread
- 8.5 mm drill → about 77% thread
- 8.6 mm drill → about 72% thread
Other pitches of M10: M10 × 1.25, M10 × 1.
Threads close in size (not interchangeable – the pitch and/or angle differ):
- M10 × 1.25 – 10 mm major, 1.25 mm pitch (20.3 TPI equivalent)
- M10 × 1 – 10 mm major, 1 mm pitch (25.4 TPI equivalent)
- G1/8 (1/8" BSP) – 9.73 mm major, 28 TPI (0.907 mm pitch)
- 3/8" UNC – 9.52 mm major, 16 TPI (1.587 mm pitch)
- 3/8" UNF – 9.52 mm major, 24 TPI (1.058 mm pitch)
Questions
What size drill for a M10 tap?
The tap drill for M10×1.5 is 8.5 mm. That’s the standard chart size and gives about 77% of full thread.
What size clearance hole for M10?
For a M10 screw or bolt, drill 10.5 mm for a close fit, 11 mm for a medium (normal) fit or 12 mm for a free fit. These are the ISO 273 fine, medium and coarse sizes.
What is the pitch of M10?
M10×1.5 has a 1.5 mm pitch (16.9 TPI equivalent), a 60° thread angle and a 10 mm major diameter.
Sources: Chart drill: the common metric coarse tapping chart. Percent values worked out from the ISO 68-1 basic profile. Clearance holes: ISO 273 (checked 25/10/2026). Values are for reference only – check your tap maker’s chart. See the disclaimer.
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