Tap Drill Chart — Metric, UNC and UNF
Select the correct drill size before tapping. This chart covers metric coarse, UNC, and UNF thread standards. Use as a guide — verify critical applications against manufacturer specifications.
Metric Coarse Tap Drill Sizes
| Thread | Pitch (mm) | Tap Drill (mm) | Close Fit (mm) |
|---|---|---|---|
| M2 | 0.4 | 1.6 | 2.2 |
| M2.5 | 0.45 | 2.05 | 2.7 |
| M3 | 0.5 | 2.5 | 3.2 |
| M3.5 | 0.6 | 2.9 | 3.7 |
| M4 | 0.7 | 3.3 | 4.3 |
| M5 | 0.8 | 4.2 | 5.3 |
| M6 | 1.0 | 5.0 | 6.4 |
| M8 | 1.25 | 6.8 | 8.4 |
| M10 | 1.5 | 8.5 | 10.5 |
| M12 | 1.75 | 10.2 | 13.0 |
| M14 | 2.0 | 12.0 | 15.0 |
| M16 | 2.0 | 14.0 | 17.0 |
| M18 | 2.5 | 15.5 | 19.0 |
| M20 | 2.5 | 17.5 | 21.0 |
| M22 | 2.5 | 19.5 | 23.0 |
| M24 | 3.0 | 21.0 | 25.0 |
| M27 | 3.0 | 24.0 | 28.0 |
| M30 | 3.5 | 26.5 | 31.0 |
| M33 | 3.5 | 29.5 | 34.0 |
| M36 | 4.0 | 32.0 | 37.0 |
UNC — Unified National Coarse
| Thread | TPI | Tap Drill | Decimal (in) |
|---|---|---|---|
| #2-56 | 56 | #50 | 0.0700 |
| #4-40 | 40 | #43 | 0.0890 |
| #6-32 | 32 | #36 | 0.1065 |
| #8-32 | 32 | #29 | 0.1360 |
| #10-24 | 24 | #25 | 0.1495 |
| 1/4-20 | 20 | #7 | 0.2010 |
| 5/16-18 | 18 | F | 0.2570 |
| 3/8-16 | 16 | 5/16 | 0.3125 |
| 7/16-14 | 14 | U | 0.3680 |
| 1/2-13 | 13 | 27/64 | 0.4219 |
| 9/16-12 | 12 | 31/64 | 0.4844 |
| 5/8-11 | 11 | 17/32 | 0.5312 |
| 3/4-10 | 10 | 21/32 | 0.6562 |
| 7/8-9 | 9 | 49/64 | 0.7656 |
| 1-8 | 8 | 7/8 | 0.8750 |
UNF — Unified National Fine
| Thread | TPI | Tap Drill | Decimal (in) |
|---|---|---|---|
| #4-48 | 48 | #42 | 0.0935 |
| #6-40 | 40 | #33 | 0.1130 |
| #8-36 | 36 | #29 | 0.1360 |
| #10-32 | 32 | #21 | 0.1590 |
| 1/4-28 | 28 | #3 | 0.2130 |
| 5/16-24 | 24 | I | 0.2720 |
| 3/8-24 | 24 | Q | 0.3320 |
| 7/16-20 | 20 | 25/64 | 0.3906 |
| 1/2-20 | 20 | 29/64 | 0.4531 |
| 9/16-18 | 18 | 33/64 | 0.5156 |
| 5/8-18 | 18 | 37/64 | 0.5781 |
| 3/4-16 | 16 | 11/16 | 0.6875 |
| 7/8-14 | 14 | 13/16 | 0.8125 |
| 1-12 | 12 | 59/64 | 0.9219 |
How to Use This Reference
Tap drill size is the drill used to remove material before threading. These sizes give approximately 75% thread engagement — the standard recommendation for most workshop applications. Drill the hole first, then tap. Always verify against a current reference standard for critical or safety-related applications.
The "Close Fit" column (metric) gives a clearance drill size — used when you want to pass a bolt through a hole rather than thread it.
Related References
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