M6 tap drill size
The tap drill for M6×1 is 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% | 5.221 mm 0.2055" | 5.2 mm (62%) | #5 0.2055" (60%) |
| 65% | 5.156 mm 0.2030" | 5.2 mm (62%) | 13/64" 0.2031" (65%) |
| 70% | 5.091 mm 0.2004" | 5.1 mm (69%) | #7 0.2010" (69%) |
| 75% | 5.026 mm 0.1979" | 5 mm (77%) | #8 0.1990" (73%) |
| 80% | 4.961 mm 0.1953" | 5 mm (77%) | #9 0.1960" (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 5.2 mm drill gives 62%. For mild steel, brass and cast iron the 5 mm is fine.
- For a blind hole with 1.5 × D thread engagement (9 mm), drill about 13 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 M6
| Fit | Drill |
|---|---|
| Close | 6.4 mm (0.252") |
| Medium (normal) | 6.6 mm (0.260") |
| Free (loose) | 7 mm (0.276") |
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.
M6 thread data
| Designation | M6×1 |
|---|---|
| Standard | ISO 68-1 basic profile, ISO 261/262 series |
| Pitch | 1 mm pitch (25.4 TPI equivalent) |
| Thread angle | 60° |
| Major diameter | 6 mm (0.236") |
| Pitch (effective) diameter | 5.35 mm (0.211") |
| Minor diameter, external | 4.773 mm (0.188") |
| Minor diameter, internal | 4.917 mm (0.194") |
| Thread depth (internal) | 0.541 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:
- 4.9 mm drill → about 85% thread
- 5 mm drill → about 77% thread
- 5.1 mm drill → about 69% thread
Threads close in size (not interchangeable – the pitch and/or angle differ):
- 0BA – 6 mm major, 1 mm pitch (25.4 TPI equivalent)
- 1/4" UNC – 6.35 mm major, 20 TPI (1.27 mm pitch)
- 1/4" UNF – 6.35 mm major, 28 TPI (0.907 mm pitch)
- 1/4" BSW – 6.35 mm major, 20 TPI (1.27 mm pitch)
- 1/4" BSF – 6.35 mm major, 26 TPI (0.977 mm pitch)
Questions
What size drill for a M6 tap?
The tap drill for M6×1 is 5 mm. That’s the standard chart size and gives about 77% of full thread.
What size clearance hole for M6?
For a M6 screw or bolt, drill 6.4 mm for a close fit, 6.6 mm for a medium (normal) fit or 7 mm for a free fit. These are the ISO 273 fine, medium and coarse sizes.
What is the pitch of M6?
M6×1 has a 1 mm pitch (25.4 TPI equivalent), a 60° thread angle and a 6 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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