Tap Drill Size Chart
The drill bit for tapping common UNC, UNF, and metric threads at about 75 percent engagement.
| Thread | Tap drill | Thread | Tap drill |
|---|---|---|---|
| 1/4-20 UNC | #7 (0.201 in) | M3 x 0.5 | 2.5 mm |
| 5/16-18 UNC | F (0.257 in) | M4 x 0.7 | 3.3 mm |
| 3/8-16 UNC | 5/16 in | M5 x 0.8 | 4.2 mm |
| 7/16-14 UNC | U (0.368 in) | M6 x 1.0 | 5.0 mm |
| 1/2-13 UNC | 27/64 in | M8 x 1.25 | 6.8 mm |
| 10-32 UNF | #21 (0.159 in) | M10 x 1.5 | 8.5 mm |
| 1/4-28 UNF | #3 (0.213 in) | M12 x 1.75 | 10.2 mm |
Metric rule of thumb: tap drill equals major diameter minus pitch. Imperial sizes are the published 75 percent engagement drills.
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