M22 tap drill size
The tap drill for M22×2.5 is 19.5 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% | 20.051 mm 0.7894" | 20 mm (62%) | 51/64" 0.7969" (54%) |
| 65% | 19.889 mm 0.7830" | 20 mm (62%) | 25/32" 0.7813" (66%) |
| 70% | 19.727 mm 0.7766" | 19.75 mm (69%) | 25/32" 0.7813" (66%) |
| 75% | 19.564 mm 0.7702" | 19.5 mm (77%) | 49/64" 0.7656" (79%) |
| 80% | 19.402 mm 0.7639" | 19.5 mm (77%) | 49/64" 0.7656" (79%) |
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 20 mm drill gives 62%. For mild steel, brass and cast iron the 19.5 mm is fine.
- For a blind hole with 1.5 × D thread engagement (33 mm), drill about 43 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 M22
| Fit | Drill |
|---|---|
| Close | 23 mm (0.906") |
| Medium (normal) | 24 mm (0.945") |
| Free (loose) | 26 mm (1.024") |
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.
M22 thread data
| Designation | M22×2.5 |
|---|---|
| Standard | ISO 68-1 basic profile, ISO 261/262 series |
| Pitch | 2.5 mm pitch (10.2 TPI equivalent) |
| Thread angle | 60° |
| Major diameter | 22 mm (0.866") |
| Pitch (effective) diameter | 20.376 mm (0.802") |
| Minor diameter, external | 18.933 mm (0.745") |
| Minor diameter, internal | 19.294 mm (0.760") |
| Thread depth (internal) | 1.353 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:
- 19.25 mm drill → about 85% thread
- 19.5 mm drill → about 77% thread
- 19.75 mm drill → about 69% thread
Other pitches of M22: M22 × 1.5.
Threads close in size (not interchangeable – the pitch and/or angle differ):
- M22 × 1.5 – 22 mm major, 1.5 mm pitch (16.9 TPI equivalent)
- 7/8" UNC – 22.22 mm major, 9 TPI (2.822 mm pitch)
- 7/8" UNF – 22.22 mm major, 14 TPI (1.814 mm pitch)
- 7/8" BSW – 22.22 mm major, 9 TPI (2.822 mm pitch)
- 7/8" BSF – 22.22 mm major, 11 TPI (2.309 mm pitch)
Questions
What size drill for a M22 tap?
The tap drill for M22×2.5 is 19.5 mm. That’s the standard chart size and gives about 77% of full thread.
What size clearance hole for M22?
For a M22 screw or bolt, drill 23 mm for a close fit, 24 mm for a medium (normal) fit or 26 mm for a free fit. These are the ISO 273 fine, medium and coarse sizes.
What is the pitch of M22?
M22×2.5 has a 2.5 mm pitch (10.2 TPI equivalent), a 60° thread angle and a 22 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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