Metric Tap Drill Size Chart — M3 to M24 (Coarse + Fine Pitch)
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Quick reference for metric tap drill sizes. Use the 75% engagement column for general shop work in steel, stainless, and aluminium. Use 60% for brittle materials (cast iron) or long-blind-hole taps where lower torque matters. Use 100% only when the application demands maximum thread strength (usually not — 75% thread is 95% of the shear strength of 100% thread with much lower tapping torque).
Formula (if you can't find your size in the chart)
Tap drill diameter (75% engagement) = Major thread diameter − Pitch
Example: M6 × 1.0 → tap drill = 6.0 − 1.0 = 5.0 mm. M8 × 1.25 → 8.0 − 1.25 = 6.75 mm (round up to 6.8 mm nominal drill).
Metric coarse pitch (standard)
| Thread | Pitch (mm) | 75% (mm) | 60% (mm) | Clearance (mm) |
|---|---|---|---|---|
| M3 | 0.50 | 2.50 | 2.65 | 3.4 |
| M4 | 0.70 | 3.30 | 3.50 | 4.5 |
| M5 | 0.80 | 4.20 | 4.40 | 5.5 |
| M6 | 1.00 | 5.00 | 5.20 | 6.6 |
| M7 | 1.00 | 6.00 | 6.20 | 7.6 |
| M8 | 1.25 | 6.80 | 7.00 | 9.0 |
| M10 | 1.50 | 8.50 | 8.80 | 11.0 |
| M12 | 1.75 | 10.20 | 10.50 | 13.5 |
| M14 | 2.00 | 12.00 | 12.40 | 15.5 |
| M16 | 2.00 | 14.00 | 14.40 | 17.5 |
| M18 | 2.50 | 15.50 | 16.00 | 20.0 |
| M20 | 2.50 | 17.50 | 18.00 | 22.0 |
| M22 | 2.50 | 19.50 | 20.00 | 24.0 |
| M24 | 3.00 | 21.00 | 21.60 | 26.0 |
Metric fine pitch
| Thread | Pitch (mm) | 75% (mm) |
|---|---|---|
| M8 × 1.0 | 1.00 | 7.00 |
| M10 × 1.0 | 1.00 | 9.00 |
| M10 × 1.25 | 1.25 | 8.75 |
| M12 × 1.25 | 1.25 | 10.75 |
| M12 × 1.5 | 1.50 | 10.50 |
| M14 × 1.5 | 1.50 | 12.50 |
| M16 × 1.5 | 1.50 | 14.50 |
| M18 × 1.5 | 1.50 | 16.50 |
| M20 × 1.5 | 1.50 | 18.50 |
| M24 × 2.0 | 2.00 | 22.00 |
Clearance holes (for bolt passage, not threading)
If you're drilling a through-hole for a bolt (not tapping), use the "Clearance" column in the first table. Close fit is listed; medium fit = +5%, free fit = +10%.
Tap type reminders
- Taper tap — 8-10 chamfered threads, starts the thread. Use first in blind holes; sufficient alone for through holes.
- Plug tap — 3-5 chamfered threads. Forms most of the thread in through holes.
- Bottoming tap — no chamfer. Finishes threading to the bottom of a blind hole.
- Spiral point (gun tap) — pushes chips forward. Best for through holes in ductile material.
- Spiral flute tap — pulls chips back up. Best for blind holes in tough material.
Common mistakes
- Using the clearance drill size for the tap drill. A 6 mm hole will not tap M6.
- Tapping without cutting oil in steel or stainless — fastest way to break a tap.
- Reversing direction too late. Reverse every half-turn in steel, every quarter-turn in stainless.
- Using M2 HSS taps in stainless steel. Use M35 (5% cobalt) minimum — M42 ideal.
Need HSS taps?
Midland Tools stocks the full Miranda HSS range in M2, M35, and M42 grades — taper, plug, bottoming, spiral-point, and spiral-flute. Browse HSS taps or WhatsApp +91 70111 82829 with the thread and material — we'll quote the right tap + cutting oil combination.
