Metric Tap & Clearance Drill Sizes
This table covers standard coarse pitch metric threads (the default — if a drawing says “M10” without specifying pitch, it means M10×1.5 coarse). For each thread size, you get the tap drill (for cutting internal threads) and clearance drill (for a bolt to pass through freely).
| Thread | Pitch (mm) | Tap Drill (mm) | Tap Drill (in approx) | Close Fit Clearance (mm) | Free Fit Clearance (mm) |
|---|---|---|---|---|---|
| M2 | 0.40 | 1.60 | 1/16″ | 2.2 | 2.4 |
| M2.5 | 0.45 | 2.05 | 5/64″ | 2.7 | 2.9 |
| M3 | 0.50 | 2.50 | 3/32″ | 3.2 | 3.4 |
| M4 | 0.70 | 3.30 | 1/8″ | 4.3 | 4.5 |
| M5 | 0.80 | 4.20 | 11/64″ | 5.3 | 5.5 |
| M6 | 1.00 | 5.00 | 13/64″ | 6.4 | 6.6 |
| M8 | 1.25 | 6.75 | 17/64″ | 8.4 | 9.0 |
| M10 | 1.50 | 8.50 | 21/64″ | 10.5 | 11.0 |
| M12 | 1.75 | 10.25 | Z (0.413″) | 13.0 | 13.5 |
| M14 | 2.00 | 12.00 | 15/32″ | 15.0 | 15.5 |
| M16 | 2.00 | 14.00 | 35/64″ | 17.0 | 17.5 |
| M18 | 2.50 | 15.50 | 39/64″ | 19.0 | 20.0 |
| M20 | 2.50 | 17.50 | 11/16″ | 21.0 | 22.0 |
| M22 | 2.50 | 19.50 | 49/64″ | 23.0 | 24.0 |
| M24 | 3.00 | 21.00 | 53/64″ | 25.0 | 26.0 |
| M27 | 3.00 | 24.00 | 15/16″ | 28.0 | 30.0 |
| M30 | 3.50 | 26.50 | 1-3/64″ | 31.0 | 33.0 |
Tap Drill Formula
If your size isn’t in the table:
Tap drill = Nominal diameter − Pitch
Example: M16×2.0 → 16 − 2 = 14.0mm tap drill ✓
This gives approximately 75% thread engagement, which is the sweet spot for most applications. Going deeper (smaller drill) increases tap breakage risk without meaningfully improving strength.
Close Fit vs. Free Fit Clearance
- Close fit: Bolt passes through with minimal play — use when alignment matters
- Free fit: Extra clearance for easy assembly, slotted holes, or when holes don’t line up perfectly
Related: UNC Tap Drill Sizes | UNF Tap Drill Sizes | Metric Hex Bolt Head Sizes