The most used tap drills: #4-40 takes a #43, #6-32 a #36, #8-32 a #29, #10-24 a #25, #10-32 a #21, 1/4-20 a #7, 5/16-18 an F, 3/8-16 a 5/16, 1/2-13 a 27/64. Metric: M3 x 0.5 takes 2.5 mm, M4 x 0.7 takes 3.3 mm, M5 x 0.8 takes 4.2 mm, M6 x 1.0 takes 5.0 mm, M8 x 1.25 takes 6.8 mm.
Every drill in this chart gives about 75% of full thread depth, the standard that published tap drill charts use because it keeps about 95% of full thread strength for roughly a third of the tapping torque. Click any thread for its own page with 60 to 80% alternatives, clearance holes and pitch diameter.
For a thread not listed, or a different percentage, use the tap drill calculator.
Tools that go with this chart
Unified inch threads (UNC and UNF)
| Thread | Series | Major dia (in) | Tap drill | Drill (in) | Drill (mm) |
|---|---|---|---|---|---|
| #0-80 | UNF | 0.0600 | 3/64" | 0.0469 | 1.19 |
| #1-64 | UNC | 0.0730 | #53 | 0.0595 | 1.51 |
| #1-72 | UNF | 0.0730 | #53 | 0.0595 | 1.51 |
| #2-56 | UNC | 0.0860 | #50 | 0.0700 | 1.78 |
| #2-64 | UNF | 0.0860 | #50 | 0.0700 | 1.78 |
| #3-48 | UNC | 0.0990 | #47 | 0.0785 | 1.99 |
| #3-56 | UNF | 0.0990 | #45 | 0.0820 | 2.08 |
| #4-40 | UNC | 0.1120 | #43 | 0.0890 | 2.26 |
| #4-48 | UNF | 0.1120 | #42 | 0.0935 | 2.37 |
| #5-40 | UNC | 0.1250 | #38 | 0.1015 | 2.58 |
| #5-44 | UNF | 0.1250 | #37 | 0.1040 | 2.64 |
| #6-32 | UNC | 0.1380 | #36 | 0.1065 | 2.71 |
| #6-40 | UNF | 0.1380 | #33 | 0.1130 | 2.87 |
| #8-32 | UNC | 0.1640 | #29 | 0.1360 | 3.45 |
| #8-36 | UNF | 0.1640 | #29 | 0.1360 | 3.45 |
| #10-24 | UNC | 0.1900 | #25 | 0.1495 | 3.80 |
| #10-32 | UNF | 0.1900 | #21 | 0.1590 | 4.04 |
| #12-24 | UNC | 0.2160 | #16 | 0.1770 | 4.50 |
| #12-28 | UNF | 0.2160 | #14 | 0.1820 | 4.62 |
| 1/4-20 | UNC | 0.2500 | #7 | 0.2010 | 5.11 |
| 1/4-28 | UNF | 0.2500 | #3 | 0.2130 | 5.41 |
| 5/16-18 | UNC | 0.3125 | F | 0.2570 | 6.53 |
| 5/16-24 | UNF | 0.3125 | I | 0.2720 | 6.91 |
| 3/8-16 | UNC | 0.3750 | 5/16" | 0.3125 | 7.94 |
| 3/8-24 | UNF | 0.3750 | Q | 0.3320 | 8.43 |
| 7/16-14 | UNC | 0.4375 | U | 0.3680 | 9.35 |
| 7/16-20 | UNF | 0.4375 | 25/64" | 0.3906 | 9.92 |
| 1/2-13 | UNC | 0.5000 | 27/64" | 0.4219 | 10.72 |
| 1/2-20 | UNF | 0.5000 | 29/64" | 0.4531 | 11.51 |
| 9/16-12 | UNC | 0.5625 | 31/64" | 0.4844 | 12.30 |
| 9/16-18 | UNF | 0.5625 | 33/64" | 0.5156 | 13.10 |
| 5/8-11 | UNC | 0.6250 | 17/32" | 0.5312 | 13.49 |
| 5/8-18 | UNF | 0.6250 | 37/64" | 0.5781 | 14.68 |
| 3/4-10 | UNC | 0.7500 | 21/32" | 0.6562 | 16.67 |
| 3/4-16 | UNF | 0.7500 | 11/16" | 0.6875 | 17.46 |
| 7/8-9 | UNC | 0.8750 | 49/64" | 0.7656 | 19.45 |
| 7/8-14 | UNF | 0.8750 | 13/16" | 0.8125 | 20.64 |
| 1-8 | UNC | 1.0000 | 7/8" | 0.8750 | 22.22 |
| 1-12 | UNF | 1.0000 | 59/64" | 0.9219 | 23.42 |
| 1-14 | UNS | 1.0000 | 15/16" | 0.9375 | 23.81 |
ISO metric threads (coarse and fine)
| Thread | Series | Pitch (mm) | Tap drill (mm) | Drill (in) |
|---|---|---|---|---|
| M1.6x0.35 | coarse | 0.35 | 1.25 | 0.0492 |
| M2x0.4 | coarse | 0.4 | 1.6 | 0.0630 |
| M2.5x0.45 | coarse | 0.45 | 2.05 | 0.0807 |
| M3x0.5 | coarse | 0.5 | 2.5 | 0.0984 |
| M3x0.35 | fine | 0.35 | 2.65 | 0.1043 |
| M3.5x0.6 | coarse | 0.6 | 2.9 | 0.1142 |
| M4x0.7 | coarse | 0.7 | 3.3 | 0.1299 |
| M4x0.5 | fine | 0.5 | 3.5 | 0.1378 |
| M5x0.8 | coarse | 0.8 | 4.2 | 0.1654 |
| M5x0.5 | fine | 0.5 | 4.5 | 0.1772 |
| M6x1 | coarse | 1 | 5 | 0.1969 |
| M6x0.75 | fine | 0.75 | 5.25 | 0.2067 |
| M8x1.25 | coarse | 1.25 | 6.8 | 0.2677 |
| M8x1 | fine | 1 | 7 | 0.2756 |
| M10x1.5 | coarse | 1.5 | 8.5 | 0.3346 |
| M10x1.25 | fine | 1.25 | 8.8 | 0.3465 |
| M10x1 | fine | 1 | 9 | 0.3543 |
| M12x1.75 | coarse | 1.75 | 10.2 | 0.4016 |
| M12x1.5 | fine | 1.5 | 10.5 | 0.4134 |
| M12x1.25 | fine | 1.25 | 10.8 | 0.4252 |
| M14x2 | coarse | 2 | 12 | 0.4724 |
| M14x1.5 | fine | 1.5 | 12.5 | 0.4921 |
| M16x2 | coarse | 2 | 14 | 0.5512 |
| M16x1.5 | fine | 1.5 | 14.5 | 0.5709 |
| M18x2.5 | coarse | 2.5 | 15.5 | 0.6102 |
| M18x1.5 | fine | 1.5 | 16.5 | 0.6496 |
| M20x2.5 | coarse | 2.5 | 17.5 | 0.6890 |
| M20x1.5 | fine | 1.5 | 18.5 | 0.7283 |
| M22x2.5 | coarse | 2.5 | 19.5 | 0.7677 |
| M22x1.5 | fine | 1.5 | 20.5 | 0.8071 |
| M24x3 | coarse | 3 | 21 | 0.8268 |
| M24x2 | fine | 2 | 22 | 0.8661 |
| M27x3 | coarse | 3 | 24 | 0.9449 |
| M30x3.5 | coarse | 3.5 | 26.5 | 1.0433 |
| M30x2 | fine | 2 | 28 | 1.1024 |
| M36x4 | coarse | 4 | 32 | 1.2598 |
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Frequently asked questions
What size drill for a 1/4-20 tap?
A #7 drill, 0.201 inch, gives the standard 75% thread. A 13/64 inch drill (0.2031) is the common fractional substitute and gives about 72%, which taps a little easier and is still plenty strong. In stainless or a blind hole, the 13/64 is the safer choice.
What size drill for an M6 tap?
For the standard M6 x 1.0 coarse thread, drill 5.0 mm. The inch substitute is a #9 (0.196 inch) or #8 (0.199); 13/64 is slightly large. For the fine M6 x 0.75, drill 5.25 mm, or 5.2 mm if that is what your set has.
Why do charts disagree by one drill size?
Some charts list the drill for 75% thread, others for about 65% (often labeled for steel or stainless), and a few round to whatever fractional drill is nearest. All are workable. This chart uses 75%, the most common basis; each thread page shows the drills for other percentages.
Keep going
Figures are from published standards and handbook values, reproduced for convenience. Check critical dimensions against the standard or your tooling manufacturer.