Tap drill size chart
Standard cut-tap drill sizes for metric coarse and fine threads, UNC and UNF, with decimal and metric equivalents and the thread percentage each drill leaves. For example, M8 × 1.25 takes a 6.8 mm drill and 1/4-20 UNC takes a #7 drill.
Metric coarse, drill index
Metric coarse
| Thread | Pitch mm | Tap drill | Inch | Thread |
|---|---|---|---|---|
| M1.6 | 0.35 | 1.25 mm | 0.0492" | 77 % |
| M2 | 0.4 | 1.6 mm | 0.0630" | 77 % |
| M2.5 | 0.45 | 2.05 mm | 0.0807" | 77 % |
| M3 | 0.5 | 2.5 mm | 0.0984" | 77 % |
| M3.5 | 0.6 | 2.9 mm | 0.1142" | 77 % |
| M4 | 0.7 | 3.3 mm | 0.1299" | 77 % |
| M5 | 0.8 | 4.2 mm | 0.1654" | 77 % |
| M6 | 1 | 5 mm | 0.1969" | 77 % |
| M8 | 1.25 | 6.8 mm | 0.2677" | 74 % |
| M10 | 1.5 | 8.5 mm | 0.3346" | 77 % |
| M12 | 1.75 | 10.2 mm | 0.4016" | 79 % |
| M14 | 2 | 12 mm | 0.4724" | 77 % |
| M16 | 2 | 14 mm | 0.5512" | 77 % |
| M18 | 2.5 | 15.5 mm | 0.6102" | 77 % |
| M20 | 2.5 | 17.5 mm | 0.6890" | 77 % |
| M22 | 2.5 | 19.5 mm | 0.7677" | 77 % |
| M24 | 3 | 21 mm | 0.8268" | 77 % |
| M27 | 3 | 24 mm | 0.9449" | 77 % |
| M30 | 3.5 | 26.5 mm | 1.0433" | 77 % |
| M33 | 3.5 | 29.5 mm | 1.1614" | 77 % |
| M36 | 4 | 32 mm | 1.2598" | 77 % |
| M39 | 4 | 35 mm | 1.3780" | 77 % |
| M42 | 4.5 | 37.5 mm | 1.4764" | 77 % |
| M48 | 5 | 43 mm | 1.6929" | 77 % |
Metric fine
| Thread | Pitch mm | Tap drill | Inch | Thread |
|---|---|---|---|---|
| M3 × 0.35 | 0.35 | 2.65 mm | 0.1043" | 77 % |
| M4 × 0.5 | 0.5 | 3.5 mm | 0.1378" | 77 % |
| M5 × 0.5 | 0.5 | 4.5 mm | 0.1772" | 77 % |
| M6 × 0.75 | 0.75 | 5.2 mm | 0.2047" | 82 % |
| M8 × 1 | 1 | 7 mm | 0.2756" | 77 % |
| M10 × 1 | 1 | 9 mm | 0.3543" | 77 % |
| M10 × 1.25 | 1.25 | 8.8 mm | 0.3465" | 74 % |
| M12 × 1.25 | 1.25 | 10.8 mm | 0.4252" | 74 % |
| M12 × 1.5 | 1.5 | 10.5 mm | 0.4134" | 77 % |
| M14 × 1.5 | 1.5 | 12.5 mm | 0.4921" | 77 % |
| M16 × 1.5 | 1.5 | 14.5 mm | 0.5709" | 77 % |
| M18 × 1.5 | 1.5 | 16.5 mm | 0.6496" | 77 % |
| M20 × 1.5 | 1.5 | 18.5 mm | 0.7283" | 77 % |
| M22 × 1.5 | 1.5 | 20.5 mm | 0.8071" | 77 % |
| M24 × 2 | 2 | 22 mm | 0.8661" | 77 % |
| M27 × 2 | 2 | 25 mm | 0.9843" | 77 % |
| M30 × 2 | 2 | 28 mm | 1.1024" | 77 % |
UNC, Unified coarse
| Thread | TPI | Drill | Inch | mm | Thread |
|---|---|---|---|---|---|
| #1-64 | 64 | #53 | 0.0595" | 1.51 mm | 67 % |
| #2-56 | 56 | #50 | 0.0700" | 1.78 mm | 69 % |
| #3-48 | 48 | #47 | 0.0785" | 1.99 mm | 76 % |
| #4-40 | 40 | #43 | 0.0890" | 2.26 mm | 71 % |
| #5-40 | 40 | #38 | 0.1015" | 2.58 mm | 72 % |
| #6-32 | 32 | #36 | 0.1065" | 2.71 mm | 78 % |
| #8-32 | 32 | #29 | 0.1360" | 3.45 mm | 69 % |
| #10-24 | 24 | #25 | 0.1495" | 3.80 mm | 75 % |
| #12-24 | 24 | #16 | 0.1770" | 4.50 mm | 72 % |
| 1/4-20 | 20 | #7 | 0.2010" | 5.11 mm | 75 % |
| 5/16-18 | 18 | F | 0.2570" | 6.53 mm | 77 % |
| 3/8-16 | 16 | 5/16 | 0.3125" | 7.94 mm | 77 % |
| 7/16-14 | 14 | U | 0.3680" | 9.35 mm | 75 % |
| 1/2-13 | 13 | 27/64 | 0.4219" | 10.72 mm | 78 % |
| 9/16-12 | 12 | 31/64 | 0.4844" | 12.30 mm | 72 % |
| 5/8-11 | 11 | 17/32 | 0.5313" | 13.50 mm | 79 % |
| 3/4-10 | 10 | 21/32 | 0.6563" | 16.67 mm | 72 % |
| 7/8-9 | 9 | 49/64 | 0.7656" | 19.45 mm | 76 % |
| 1-8 | 8 | 7/8 | 0.8750" | 22.22 mm | 77 % |
UNF, Unified fine
| Thread | TPI | Drill | Inch | mm | Thread |
|---|---|---|---|---|---|
| #0-80 | 80 | 3/64 | 0.0469" | 1.19 mm | 81 % |
| #1-72 | 72 | #53 | 0.0595" | 1.51 mm | 75 % |
| #2-64 | 64 | #50 | 0.0700" | 1.78 mm | 79 % |
| #3-56 | 56 | #45 | 0.0820" | 2.08 mm | 73 % |
| #4-48 | 48 | #42 | 0.0935" | 2.37 mm | 68 % |
| #5-44 | 44 | #37 | 0.1040" | 2.64 mm | 71 % |
| #6-40 | 40 | #33 | 0.1130" | 2.87 mm | 77 % |
| #8-36 | 36 | #29 | 0.1360" | 3.45 mm | 78 % |
| #10-32 | 32 | #21 | 0.1590" | 4.04 mm | 76 % |
| #12-28 | 28 | #14 | 0.1820" | 4.62 mm | 73 % |
| 1/4-28 | 28 | #3 | 0.2130" | 5.41 mm | 80 % |
| 5/16-24 | 24 | I | 0.2720" | 6.91 mm | 75 % |
| 3/8-24 | 24 | Q | 0.3320" | 8.43 mm | 79 % |
| 7/16-20 | 20 | 25/64 | 0.3906" | 9.92 mm | 72 % |
| 1/2-20 | 20 | 29/64 | 0.4531" | 11.51 mm | 72 % |
| 9/16-18 | 18 | 33/64 | 0.5156" | 13.10 mm | 65 % |
| 5/8-18 | 18 | 37/64 | 0.5781" | 14.68 mm | 65 % |
| 3/4-16 | 16 | 11/16 | 0.6875" | 17.46 mm | 77 % |
| 7/8-14 | 14 | 13/16 | 0.8125" | 20.64 mm | 67 % |
| 1-12 | 12 | 59/64 | 0.9219" | 23.42 mm | 72 % |
How much thread you need
Thread percentage to aim for by material.
Mild and alloy steel65–75 % thread
Stainless steel60–70 % thread
Cast iron70–80 % thread
Aluminium75–85 % thread
Brass and bronze75–85 % thread
Plastics75–85 % thread
Bars run from 50 % to 90 % thread. Typical shop practice for cut taps. Harder, tougher materials take less thread to save the tap; soft materials need more engagement to hold.