M12 tap drill size
The tap drill for M12×1.75 is 10.2 mm. That’s the standard chart size and gives about 79% 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% | 10.636 mm 0.4187" | 10.6 mm (62%) | 27/64" 0.4219" (56%) |
| 65% | 10.522 mm 0.4143" | 10.5 mm (66%) | letter Z 0.4130" (66%) |
| 70% | 10.409 mm 0.4098" | 10.4 mm (70%) | letter Z 0.4130" (66%) |
| 75% | 10.295 mm 0.4053" | 10.3 mm (75%) | 13/32" 0.4063" (74%) |
| 80% | 10.181 mm 0.4008" | 10.2 mm (79%) | letter Y 0.4040" (76%) |
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 10.5 mm drill gives 66%. For mild steel, brass and cast iron the 10.2 mm is fine.
- For a blind hole with 1.5 × D thread engagement (18 mm), drill about 25 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 M12
| Fit | Drill |
|---|---|
| Close | 13 mm (0.512") |
| Medium (normal) | 13.5 mm (0.531") |
| Free (loose) | 14.5 mm (0.571") |
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.
M12 thread data
| Designation | M12×1.75 |
|---|---|
| Standard | ISO 68-1 basic profile, ISO 261/262 series |
| Pitch | 1.75 mm pitch (14.5 TPI equivalent) |
| Thread angle | 60° |
| Major diameter | 12 mm (0.472") |
| Pitch (effective) diameter | 10.863 mm (0.428") |
| Minor diameter, external | 9.853 mm (0.388") |
| Minor diameter, internal | 10.106 mm (0.398") |
| Thread depth (internal) | 0.947 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:
- 10.2 mm drill → about 79% thread
- 10.3 mm drill → about 75% thread
- 10.4 mm drill → about 70% thread
Other pitches of M12: M12 × 1.5, M12 × 1.25.
Threads close in size (not interchangeable – the pitch and/or angle differ):
- M12 × 1.5 – 12 mm major, 1.5 mm pitch (16.9 TPI equivalent)
- M12 × 1.25 – 12 mm major, 1.25 mm pitch (20.3 TPI equivalent)
- 1/2" UNC – 12.7 mm major, 13 TPI (1.954 mm pitch)
- 1/2" UNF – 12.7 mm major, 20 TPI (1.27 mm pitch)
- 1/2" BSW – 12.7 mm major, 12 TPI (2.117 mm pitch)
Questions
What size drill for a M12 tap?
The tap drill for M12×1.75 is 10.2 mm. That’s the standard chart size and gives about 79% of full thread.
What size clearance hole for M12?
For a M12 screw or bolt, drill 13 mm for a close fit, 13.5 mm for a medium (normal) fit or 14.5 mm for a free fit. These are the ISO 273 fine, medium and coarse sizes.
What is the pitch of M12?
M12×1.75 has a 1.75 mm pitch (14.5 TPI equivalent), a 60° thread angle and a 12 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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