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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