Tap drill sizes for common threads
Tap drill, decimal and metric size, percent of thread and clearance hole for UNC, UNF, metric and NPT threads. Pick a thread for the full sheet.
UNC coarse Full chart
| Thread | Drill | Inch |
|---|---|---|
| #2-56 | #50 | 0.0700 |
| #4-40 | #43 | 0.0890 |
| #6-32 | #36 | 0.1065 |
| #8-32 | #29 | 0.1360 |
| #10-24 | #25 | 0.1495 |
| #12-24 | #16 | 0.1770 |
| 1/4-20 | #7 | 0.2010 |
| 5/16-18 | F | 0.2570 |
| 3/8-16 | 5/16" | 0.3125 |
| 7/16-14 | U | 0.3680 |
| 1/2-13 | 27/64" | 0.4219 |
| 5/8-11 | 17/32" | 0.5313 |
| 3/4-10 | 21/32" | 0.6563 |
UNF fine Full chart
| Thread | Drill | Inch |
|---|---|---|
| #10-32 | #21 | 0.1590 |
| 1/4-28 | #3 | 0.2130 |
| 5/16-24 | I | 0.2720 |
| 3/8-24 | Q | 0.3320 |
| 7/16-20 | 25/64" | 0.3906 |
| 1/2-20 | 29/64" | 0.4531 |
| 5/8-18 | 37/64" | 0.5781 |
| 3/4-16 | 11/16" | 0.6875 |
Metric Full chart
| Thread | Drill | Inch |
|---|---|---|
| M2 x 0.4 | 1.6 mm | 0.0630 |
| M3 x 0.5 | 2.5 mm | 0.0984 |
| M4 x 0.7 | 3.3 mm | 0.1299 |
| M5 x 0.8 | 4.2 mm | 0.1654 |
| M6 x 1 | 5 mm | 0.1969 |
| M8 x 1.25 | 6.8 mm | 0.2677 |
| M10 x 1.5 | 8.5 mm | 0.3347 |
| M12 x 1.75 | 10.2 mm | 0.4016 |
| M16 x 2 | 14 mm | 0.5512 |
| Fine pitch | ||
| M8 x 1 | 7 mm | 0.2756 |
| M10 x 1.25 | 8.8 mm | 0.3465 |
| M10 x 1 | 9 mm | 0.3543 |
| M12 x 1.5 | 10.5 mm | 0.4134 |
NPT pipe Full chart
| Thread | Drill | Inch |
|---|---|---|
| 1/8" | R | 0.3390 |
| 1/4" | 7/16" | 0.4375 |
| 3/8" | 37/64" | 0.5781 |
| 1/2" | 23/32" | 0.7188 |
| 3/4" | 59/64" | 0.9219 |
| 1" | 1-5/32" | 1.1563 |
Drills are the size closest to 75% thread. Sizes are calculated from ASME B1.1, ISO 261/965-1 and ASME B1.20.1, then checked against published tap drill charts.