Free tool
Tap and drill size chart
Metric threads (ISO, coarse pitch). Pick a size for the tap drill and clearance drill, or scan the full table below right away.
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Full table — M2 through M24
| Size | Pitch | Tap drill 75% | Tap drill 50% | Clearance close | Clearance free |
|---|---|---|---|---|---|
| M2 | 0.4 mm | Ø 1.6 mm | Ø 1.73 mm | Ø 2.2 mm | Ø 2.5 mm |
| M2.5 | 0.45 mm | Ø 2.05 mm | Ø 2.2 mm | Ø 2.7 mm | Ø 3 mm |
| M3 | 0.5 mm | Ø 2.5 mm | Ø 2.67 mm | Ø 3.2 mm | Ø 3.5 mm |
| M4 | 0.7 mm | Ø 3.3 mm | Ø 3.53 mm | Ø 4.2 mm | Ø 4.5 mm |
| M5 | 0.8 mm | Ø 4.2 mm | Ø 4.47 mm | Ø 5.2 mm | Ø 5.5 mm |
| M6 | 1 mm | Ø 5 mm | Ø 5.33 mm | Ø 6.2 mm | Ø 6.5 mm |
| M8 | 1.25 mm | Ø 6.75 mm | Ø 7.17 mm | Ø 8.2 mm | Ø 8.5 mm |
| M10 | 1.5 mm | Ø 8.5 mm | Ø 9 mm | Ø 10.2 mm | Ø 10.5 mm |
| M12 | 1.75 mm | Ø 10.25 mm | Ø 10.83 mm | Ø 12.2 mm | Ø 12.5 mm |
| M14 | 2 mm | Ø 12 mm | Ø 12.67 mm | Ø 14.2 mm | Ø 14.5 mm |
| M16 | 2 mm | Ø 14 mm | Ø 14.67 mm | Ø 16.2 mm | Ø 16.5 mm |
| M18 | 2.5 mm | Ø 15.5 mm | Ø 16.33 mm | Ø 18.2 mm | Ø 18.5 mm |
| M20 | 2.5 mm | Ø 17.5 mm | Ø 18.33 mm | Ø 20.2 mm | Ø 20.5 mm |
| M22 | 2.5 mm | Ø 19.5 mm | Ø 20.33 mm | Ø 22.2 mm | Ø 22.5 mm |
| M24 | 3 mm | Ø 21 mm | Ø 22 mm | Ø 24.2 mm | Ø 24.5 mm |
The formula
At 75% thread engagement — the standard published on virtually every machinist's chart — the tap drill is simply the diameter minus the pitch:
tap drill diameter (75%) = nominal diameter − pitch
For any other engagement percentage, this tool scales that deduction proportionally from that 75% anchor point:
tap drill diameter (%) = nominal diameter − pitch × (engagement % / 75)
75% engagement is the common choice for softer materials (aluminium, brass, plastic) — strong enough, and easier to tap. In steel and stainless, 50% is often already strong enough and saves the tap itself unnecessary force and wear.
The clearance drill (for a through hole with a bolt, no thread) is a rule of thumb here — close: diameter + 0.2 mm, free: diameter + 0.5 mm — not an official ISO fit table. For a critical fit, check the exact class (H12/H13).
Not sure about the right size for your part?Send your drawing