Guides / Shop charts · Updated
Tap drill chart
For about 75% thread, the usual target. From Drill America's and Irwin's charts; where they differ, both are shown.
Short answer
A 1/4-20 tap takes a #7 drill (.2010 in), 5/16-18 an F, 3/8-16 a 5/16 in and 1/2-13 a 27/64 in. An M6 × 1.0 tap takes a 5 mm drill, and M8 × 1.25 takes 6.75 mm.
Unified inch threads (UNC and UNF)
| Thread | Tap drill | Decimal |
|---|---|---|
| #4-40 UNC | #43 | .0890 |
| #4-48 UNF | #42 or 3/32 Drill America #42, Irwin 3/32 | .0935 |
| #5-40 UNC | #38 | .1015 |
| #5-44 UNF | #37 | .1040 |
| #6-32 UNC | #36 | .1065 |
| #6-40 UNF | #33 | .1130 |
| #8-32 UNC | #29 | .1360 |
| #8-36 UNF | #29 Irwin only | .1360 |
| #10-24 UNC | #25 | .1495 |
| #10-32 UNF | #21 | .1590 |
| #12-24 UNC | #16 | .1770 |
| #12-28 UNF | #14 | .1820 |
| 1/4-20 UNC | #7 | .2010 |
| 1/4-28 UNF | #3 | .2130 |
| 5/16-18 UNC | F | .2570 |
| 5/16-24 UNF | I | .2720 |
| 3/8-16 UNC | 5/16 | .3125 |
| 3/8-24 UNF | Q | .3320 |
| 7/16-14 UNC | U | .3680 |
| 7/16-20 UNF | 25/64 | .3906 |
| 1/2-13 UNC | 27/64 | .4219 |
| 1/2-20 UNF | 29/64 | .4531 |
| 9/16-12 UNC | 31/64 | .4844 |
| 9/16-18 UNF | 33/64 | .5156 |
| 5/8-11 UNC | 17/32 | .5312 |
| 5/8-18 UNF | 37/64 | .5781 |
| 3/4-10 UNC | 21/32 | .6562 |
| 3/4-16 UNF | 11/16 | .6875 |
| 7/8-9 UNC | 49/64 or 25/32 Drill America 49/64 (.7656), Irwin 25/32 (.7812) | - |
| 7/8-14 UNF | 13/16 | .8125 |
| 1-8 UNC | 7/8 | .8750 |
| 1-12 UNF | 59/64 Irwin only | .9219 |
Metric coarse threads
| Thread | Tap drill | Decimal in | Inch drill (Irwin) |
|---|---|---|---|
| M3 × 0.5 | 2.5 mm | .0984 | - |
| M3.5 × 0.6 | 2.9 mm Drill America only | .1142 | - |
| M4 × 0.7 | 3.3 mm | .1299 | #30 |
| M5 × 0.8 | 4.2 mm | .1654 | #19 |
| M6 × 1.0 | 5 mm | .1969 | #8 |
| M8 × 1.25 | 6.75 mm | .2657 | 17/64 |
| M10 × 1.5 | 8.5 mm | .3346 | R |
| M12 × 1.75 | 10 mm Irwin gives 13/32 (.4062) | .3937 | - |
| M14 × 2.0 | 12 mm | .4724 | 15/32 |
| M16 × 2.0 | 14 mm | .5512 | 35/64 |
| M18 × 2.5 | 15.5 mm | .6102 | 39/64 |
| M20 × 2.5 | 17.5 mm | .6890 | 11/16 |
| M22 × 2.5 | 19.5 mm Drill America only | .7677 | - |
| M24 × 3.0 | 21 mm | .8268 | 53/64 |
Irwin often swaps in the nearest inch drill for a metric tap. They're within about 0.1 mm, close enough for most work.
More shop charts
Building a bench to use them on? Workbench height calculator. Decimal sizes for every drill: drill bit size chart. Inch and metric wrenches: wrench size chart.