Tap & Clearance Drill Sizes — Metric
ISO metric tap and clearance drill sizes. 75% thread (aluminum, brass, plastics) and 50% thread (steel, stainless, iron) tap drills plus H11 Close Fit and H12 Free Fit clearance drills for every coarse and fine metric thread from M1.6 up to M30.
Reference
Tap and clearance drill sizes for ISO metric threads — coarse and fine pitch. All values in millimeters. 75% thread drills are used for soft materials (aluminum, brass, plastics) where chip flow matters more than holding strength. 50% thread drills are preferred for steels and stainless where keeping tap torque low prevents breakage. Close Fit (H11) clearance holes are for precision assemblies; Free Fit (H12) allows modest misalignment.
| Screw Size | Major Diameter | Pitch (mm) | Minor Diameter | Tap Drill | Clearance Drill | ||
|---|---|---|---|---|---|---|---|
| 75% Thread Al · Brass · Plastics | 50% Thread Steel · Stainless · Iron | Close Fit ISO H11 | Free Fit ISO H12 | ||||
| mm | mm | mm | mm | ||||
| M1.6 | 1.600 | 0.35 | 1.221 | 1.25 | 1.30 | 1.8 | 2.0 |
| M2 | 2.000 | 0.40 | 1.567 | 1.60 | 1.65 | 2.2 | 2.4 |
| 0.25 | 1.729 | 1.75 | 1.80 | ||||
| M2.5 | 2.500 | 0.45 | 2.013 | 2.05 | 2.10 | 2.7 | 2.9 |
| 0.35 | 2.121 | 2.15 | 2.20 | ||||
| M3 | 3.000 | 0.50 | 2.459 | 2.50 | 2.55 | 3.2 | 3.4 |
| 0.35 | 2.621 | 2.65 | 2.70 | ||||
| M3.5 | 3.500 | 0.60 | 2.851 | 2.90 | 2.95 | 3.7 | 3.9 |
| 0.35 | 3.121 | 3.15 | 3.20 | ||||
| M4 | 4.000 | 0.70 | 3.242 | 3.30 | 3.40 | 4.3 | 4.5 |
| 0.50 | 3.459 | 3.50 | 3.55 | ||||
| M5 | 5.000 | 0.80 | 4.134 | 4.20 | 4.30 | 5.3 | 5.5 |
| 0.50 | 4.459 | 4.50 | 4.55 | ||||
| M6 | 6.000 | 1.00 | 4.918 | 5.00 | 5.20 | 6.4 | 6.6 |
| 0.75 | 5.188 | 5.25 | 5.40 | ||||
| M7 | 7.000 | 1.00 | 5.918 | 6.00 | 6.20 | 7.4 | 7.6 |
| 0.75 | 6.188 | 6.25 | 6.40 | ||||
| M8 | 8.000 | 1.25 | 6.647 | 6.80 | 6.90 | 8.4 | 9.0 |
| 1.00 | 6.918 | 7.00 | 7.20 | ||||
| M10 | 10.000 | 1.50 | 8.376 | 8.50 | 8.70 | 10.5 | 11.0 |
| 1.25 | 8.647 | 8.80 | 9.00 | ||||
| 1.00 | 8.918 | 9.00 | 9.20 | ||||
| M12 | 12.000 | 1.75 | 10.106 | 10.20 | 10.40 | 13.0 | 13.5 |
| 1.50 | 10.376 | 10.50 | 10.70 | ||||
| 1.25 | 10.647 | 10.80 | 11.00 | ||||
| M14 | 14.000 | 2.00 | 11.835 | 12.00 | 12.20 | 15.0 | 15.5 |
| 1.50 | 12.376 | 12.50 | 12.70 | ||||
| M16 | 16.000 | 2.00 | 13.835 | 14.00 | 14.25 | 17.0 | 17.5 |
| 1.50 | 14.376 | 14.50 | 14.75 | ||||
| M18 | 18.000 | 2.50 | 15.294 | 15.50 | 15.75 | 19.0 | 20.0 |
| 2.00 | 15.835 | 16.00 | 16.25 | ||||
| 1.50 | 16.376 | 16.50 | 16.75 | ||||
| M20 | 20.000 | 2.50 | 17.294 | 17.50 | 17.75 | 21.0 | 22.0 |
| 2.00 | 17.835 | 18.00 | 18.25 | ||||
| 1.50 | 18.376 | 18.50 | 18.75 | ||||
| M22 | 22.000 | 2.50 | 19.294 | 19.50 | 19.75 | 23.0 | 24.0 |
| 2.00 | 19.835 | 20.00 | 20.25 | ||||
| 1.50 | 20.376 | 20.50 | 20.75 | ||||
| M24 | 24.000 | 3.00 | 20.752 | 21.00 | 21.25 | 25.0 | 26.0 |
| 2.00 | 21.835 | 22.00 | 22.25 | ||||
| M27 | 27.000 | 3.00 | 23.752 | 24.00 | 24.25 | 28.0 | 30.0 |
| 2.00 | 24.835 | 25.00 | 25.25 | ||||
| M30 | 30.000 | 3.50 | 26.211 | 26.50 | 26.75 | 31.0 | 33.0 |
| 2.00 | 27.835 | 28.00 | 28.25 | ||||
How to read this chart
- Pick your metric size (e.g. M6) then find the row matching your thread pitch (coarse: M6 × 1.0 is default; fine: M6 × 0.75 for thin-wall applications).
- Choose between the 75% thread and 50% thread columns based on material. 75% is full-strength standard; 50% cuts tap torque and is the production default.
- Use a metric drill set. Sizes given in 0.05 mm steps match standard tool-room drills.
- Always deburr and chamfer holes before tapping. Use cutting fluid on steel / stainless — neat kerosene on aluminum — dry on cast iron.
- For through-hole assembly, drill the other piece to the Close or Free Fit column.
Metric tap drill formulas
- 75% thread
- Tap Dia = Major − pitch. Example: M6 × 1.0 → 6 − 1 = 5.0 mm.
- 50% thread
- Tap Dia ≈ Major − 1.3·pitch. Example: M6 × 1.0 → 6 − 1.3 = 4.7 mm (round up to nearest standard drill).
- Minor diameter
- d_minor = d − 1.0825·pitch (theoretical minor). The minor column is informational — don't use it as the tap drill.
- Clearance H11 / H12
- ISO 273: H11 (Close) ≈ major + 0.3-0.5 mm · H12 (Free) ≈ major + 0.6-1.0 mm.
Notes
- Metric data derived from ISO 262 (threads) and ISO 273 (clearance holes). Pair this with the Imperial Tap & Clearance Drill Sizes chart for mixed-unit work.
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