M3 tap drill size
The tap drill for M3×0.5 is 2.5 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% | 2.61 mm 0.1028" | 2.6 mm (62%) | #37 0.1040" (55%) |
| 65% | 2.578 mm 0.1015" | 2.6 mm (62%) | #38 0.1015" (65%) |
| 70% | 2.545 mm 0.1002" | 2.55 mm (69%) | #39 0.0995" (73%) |
| 75% | 2.513 mm 0.0989" | 2.5 mm (77%) | #39 0.0995" (73%) |
| 80% | 2.48 mm 0.0977" | 2.5 mm (77%) | #40 0.0980" (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.
- Taps this small snap easily. By hand, or in stainless steel, a 2.6 mm drill (about 62% thread) makes tapping much easier for very little loss of strength.
- For a blind hole with 1.5 × D thread engagement (4.5 mm), drill about 6.5 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 M3
| Fit | Drill |
|---|---|
| Close | 3.2 mm (0.126") |
| Medium (normal) | 3.4 mm (0.134") |
| Free (loose) | 3.6 mm (0.142") |
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.
M3 thread data
| Designation | M3×0.5 |
|---|---|
| Standard | ISO 68-1 basic profile, ISO 261/262 series |
| Pitch | 0.5 mm pitch (50.8 TPI equivalent) |
| Thread angle | 60° |
| Major diameter | 3 mm (0.118") |
| Pitch (effective) diameter | 2.675 mm (0.105") |
| Minor diameter, external | 2.387 mm (0.094") |
| Minor diameter, internal | 2.459 mm (0.097") |
| Thread depth (internal) | 0.271 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:
- 2.45 mm drill → about 85% thread
- 2.5 mm drill → about 77% thread
- 2.55 mm drill → about 69% thread
Threads close in size (not interchangeable – the pitch and/or angle differ):
- #4 UNC – 2.84 mm major, 40 TPI (0.635 mm pitch)
- #4 UNF – 2.84 mm major, 48 TPI (0.529 mm pitch)
- 1/8" BSW – 3.17 mm major, 40 TPI (0.635 mm pitch)
- 5BA – 3.2 mm major, 0.59 mm pitch (43.1 TPI equivalent)
- 6BA – 2.8 mm major, 0.53 mm pitch (47.9 TPI equivalent)
Questions
What size drill for a M3 tap?
The tap drill for M3×0.5 is 2.5 mm. That’s the standard chart size and gives about 77% of full thread.
What size clearance hole for M3?
For a M3 screw or bolt, drill 3.2 mm for a close fit, 3.4 mm for a medium (normal) fit or 3.6 mm for a free fit. These are the ISO 273 fine, medium and coarse sizes.
What is the pitch of M3?
M3×0.5 has a 0.5 mm pitch (50.8 TPI equivalent), a 60° thread angle and a 3 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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