M30 tap drill size
The tap drill for M30×3.5 is 26.5 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% | 27.272 mm 1.0737" | 27.25 mm (60%) | 1-5/64" 1.0781" (58%) |
| 65% | 27.045 mm 1.0648" | 27 mm (66%) | 1-1/16" 1.0625" (66%) |
| 70% | 26.817 mm 1.0558" | 26.75 mm (71%) | 1-1/16" 1.0625" (66%) |
| 75% | 26.59 mm 1.0469" | 26.5 mm (77%) | 1-3/64" 1.0469" (75%) |
| 80% | 26.363 mm 1.0379" | 26.25 mm (82%) | 1-1/32" 1.0313" (84%) |
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 27 mm drill gives 66%. For mild steel, brass and cast iron the 26.5 mm is fine.
- At this size many people bore the hole and screwcut the thread on the lathe instead of using a hand tap. See the thread calculator for depths and the infeed.
- For a blind hole with 1.5 × D thread engagement (45 mm), drill about 59 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 M30
| Fit | Drill |
|---|---|
| Close | 31 mm (1.220") |
| Medium (normal) | 33 mm (1.299") |
| Free (loose) | 35 mm (1.378") |
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.
M30 thread data
| Designation | M30×3.5 |
|---|---|
| Standard | ISO 68-1 basic profile, ISO 261/262 series |
| Pitch | 3.5 mm pitch (7.3 TPI equivalent) |
| Thread angle | 60° |
| Major diameter | 30 mm (1.181") |
| Pitch (effective) diameter | 27.727 mm (1.092") |
| Minor diameter, external | 25.706 mm (1.012") |
| Minor diameter, internal | 26.211 mm (1.032") |
| Thread depth (internal) | 1.894 mm |
Basic sizes. Real screws are slightly under and real nuts slightly over these values because of tolerance classes.
Quick calculator
Nearest alternatives
If you don’t have the right drill, these give:
- 26.25 mm drill → about 82% thread
- 26.5 mm drill → about 77% thread
- 26.75 mm drill → about 71% thread
Other pitches of M30: M30 × 2.
Threads close in size (not interchangeable – the pitch and/or angle differ):
- M30 × 2 – 30 mm major, 2 mm pitch (12.7 TPI equivalent)
- M27 × 2 – 27 mm major, 2 mm pitch (12.7 TPI equivalent)
Questions
What size drill for a M30 tap?
The tap drill for M30×3.5 is 26.5 mm. That’s the standard chart size and gives about 77% of full thread.
What size clearance hole for M30?
For a M30 screw or bolt, drill 31 mm for a close fit, 33 mm for a medium (normal) fit or 35 mm for a free fit. These are the ISO 273 fine, medium and coarse sizes.
What is the pitch of M30?
M30×3.5 has a 3.5 mm pitch (7.3 TPI equivalent), a 60° thread angle and a 30 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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