Tap drill chart
Tap drill sizes for every common UNC, UNF and metric coarse thread, at 75% thread (the shop default) and 50% thread for hard or gummy material, with screw thread insert (STI) drills.
| Thread | 75% thread drill | Decimal (in) | 50% thread drill | Decimal (in) | STI drill |
|---|---|---|---|---|---|
| #1-64 | #53 | 0.0595 | #52 | 0.0635 | #43 |
| #2-56 | #50 | 0.0700 | #49 | 0.0730 | #41 |
| #3-48 | #47 | 0.0785 | #44 | 0.0860 | #37 |
| #4-40 | #43 | 0.0890 | #41 | 0.0960 | #31 |
| #5-40 | #38 | 0.1015 | #36 | 0.1065 | #29 |
| #6-32 | #36 | 0.1065 | #32 | 0.1160 | #25 |
| #8-32 | #29 | 0.1360 | #27 | 0.1440 | #18 |
| #10-24 | #25 | 0.1495 | #20 | 0.1610 | #10 |
| #10-32 | #21 | 0.1590 | #16 | 0.1770 | #3 |
| 1/4-20 | #7 | 0.2010 | 7/32" | 0.2188 | F |
| 5/16-18 | F | 0.2570 | G | 0.2610 | Q |
| 3/8-16 | 5/16" | 0.3125 | Q | 0.3320 | 25/64" |
| 7/16-14 | U | 0.3680 | 25/64" | 0.3906 | 29/64" |
| 1/2-13 | 27/64" | 0.4219 | 29/64" | 0.4531 | 33/64" |
| 5/8-11 | 17/32" | 0.5312 | 9/16" | 0.5625 | 41/64" |
| 3/4-10 | 21/32" | 0.6562 | 11/16" | 0.6875 | 49/64" |
| 7/8-9 | 49/64" | 0.7656 | 51/64" | 0.7969 | 57/64" |
| 1"-8 | 7/8" | 0.8750 | 59/64" | 0.9219 | 1-1/64" |
| Thread | 75% thread drill | Decimal (in) | 50% thread drill | Decimal (in) | STI drill |
|---|---|---|---|---|---|
| #0-80 | 3/64" | 0.0469 | #55 | 0.0520 | #49 |
| #1-72 | #53 | 0.0595 | #52 | 0.0635 | #45 |
| #2-64 | #50 | 0.0700 | #48 | 0.0760 | #42 |
| #4-48 | #42 | 0.0935 | #40 | 0.0980 | #27 |
| #6-40 | #33 | 0.1130 | #31 | 0.1200 | #19 |
| #8-36 | #29 | 0.1360 | #27 | 0.1440 | #13 |
| #10-32 | #21 | 0.1590 | #16 | 0.1770 | #3 |
| 1/4-28 | #3 | 0.2130 | 7/32" | 0.2188 | H |
| 5/16-24 | I | 0.2720 | J | 0.2770 | S |
| 3/8-24 | Q | 0.3320 | S | 0.3480 | 27/64" |
| 7/16-20 | W | 0.3860 | X | 0.3970 | 31/64" |
| 1/2-20 | 29/64" | 0.4531 | 15/32" | 0.4688 | 35/64" |
| 9/16-18 | 33/64" | 0.5156 | 17/32" | 0.5312 | 39/64" |
| 3/4-16 | 11/16" | 0.6875 | 45/64" | 0.7031 | 53/64" |
| Thread | 75% thread drill | Decimal (mm) | 50% thread drill | Decimal (mm) | STI drill |
|---|---|---|---|---|---|
| M3×0.5 | 2.5mm | 2.50 | 2.6mm | 2.60 | 3.4mm |
| M4×0.7 | 3.3mm | 3.30 | 3.5mm | 3.50 | 4.5mm |
| M5×0.8 | 4.2mm | 4.20 | 4.4mm | 4.40 | 5.6mm |
| M6×1.0 | 5.0mm | 5.00 | 5.2mm | 5.20 | 6.7mm |
| M8×1.25 | 6.8mm | 6.80 | 7.1mm | 7.10 | 9.0mm |
| M10×1.5 | 8.5mm | 8.50 | 8.8mm | 8.80 | 10.7mm |
| M12×1.75 | 10.2mm | 10.20 | 10.5mm | 10.50 | 12.8mm |
| M14×2.0 | 12.0mm | 12.00 | 12.5mm | 12.50 | 15.0mm |
| M16×2.0 | 14.0mm | 14.00 | 14.5mm | 14.50 | 17.0mm |
| M20×2.5 | 17.5mm | 17.50 | 18.0mm | 18.00 | 21.5mm |
| M24×3.0 | 21.0mm | 21.00 | 21.5mm | 21.50 | 25.5mm |
Common questions
- What size drill for a 1/4-20 tap?
- A #7 drill (0.201 in) gives about 75% thread. For tough material a 50% thread uses a larger drill; see the 1/4-20 row.
- What size drill for an M6×1.0 tap?
- A 5.0 mm drill gives about 75% thread for M6×1.0.
- Why 75% thread?
- 75% thread engagement keeps most of the strength while reducing tap torque and breakage; going higher adds little strength and a lot of risk.