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Tap drill chart: UNC and UNF
Recommended drills for about 75% thread engagement, calculated from ASME B1.1 thread dimensions.
| Thread | Series | Tap drill | Decimal (in) | mm | % thread | Metric alt. |
|---|---|---|---|---|---|---|
| #0-80 | UNF | 3/64 | 0.0469 | 1.19 | 81% | 1.2 mm |
| #1-64 | UNC | #53 | 0.0595 | 1.51 | 67% | 1.5 mm |
| #1-72 | UNF | #53 | 0.0595 | 1.51 | 75% | 1.5 mm |
| #2-56 | UNC | #50 | 0.0700 | 1.78 | 69% | 1.8 mm |
| #2-64 | UNF | #50 | 0.0700 | 1.78 | 79% | 1.8 mm |
| #3-48 | UNC | #47 | 0.0785 | 1.99 | 76% | 2 mm |
| #3-56 | UNF | #45 | 0.0820 | 2.08 | 73% | 2.1 mm |
| #4-40 | UNC | #43 | 0.0890 | 2.26 | 71% | 2.3 mm |
| #4-48 | UNF | #42 | 0.0935 | 2.38 | 68% | 2.4 mm |
| #5-40 | UNC | #38 | 0.1015 | 2.58 | 72% | 2.6 mm |
| #5-44 | UNF | #37 | 0.1040 | 2.64 | 71% | 2.6 mm |
| #6-32 | UNC | #36 | 0.1065 | 2.71 | 78% | 2.7 mm |
| #6-40 | UNF | #33 | 0.1130 | 2.87 | 77% | 2.9 mm |
| #8-32 | UNC | #29 | 0.1360 | 3.45 | 69% | 3.5 mm |
| #8-36 | UNF | #29 | 0.1360 | 3.45 | 78% | 3.5 mm |
| #10-24 | UNC | #25 | 0.1495 | 3.80 | 75% | 3.8 mm |
| Thread | Series | Tap drill | Decimal (in) | mm | % thread | Metric alt. |
|---|---|---|---|---|---|---|
| #10-32 | UNF | #21 | 0.1590 | 4.04 | 76% | 4 mm |
| #12-24 | UNC | #16 | 0.1770 | 4.50 | 72% | 4.5 mm |
| #12-28 | UNF | #14 | 0.1820 | 4.62 | 73% | 4.6 mm |
| 1/4-20 | UNC | #7 | 0.2010 | 5.11 | 75% | 5.1 mm |
| 1/4-28 | UNF | #3 | 0.2130 | 5.41 | 80% | 5.4 mm |
| 5/16-18 | UNC | F | 0.2570 | 6.53 | 77% | 6.5 mm |
| 5/16-24 | UNF | I | 0.2720 | 6.91 | 75% | 6.9 mm |
| 3/8-16 | UNC | 5/16 | 0.3125 | 7.94 | 77% | 7.9 mm |
| 3/8-24 | UNF | Q | 0.3320 | 8.43 | 79% | 8.4 mm |
| 7/16-14 | UNC | U | 0.3680 | 9.35 | 75% | 9.3 mm |
| 7/16-20 | UNF | 25/64 | 0.3906 | 9.92 | 72% | 9.9 mm |
| 1/2-13 | UNC | 27/64 | 0.4219 | 10.72 | 78% | 10.7 mm |
| 1/2-20 | UNF | 29/64 | 0.4531 | 11.51 | 72% | 11.5 mm |
| 9/16-12 | UNC | 31/64 | 0.4844 | 12.30 | 72% | 12.3 mm |
| 9/16-18 | UNF | 33/64 | 0.5156 | 13.10 | 65% | 13 mm |
| 5/8-11 | UNC | 17/32 | 0.5313 | 13.49 | 79% | 13.5 mm |
| 5/8-18 | UNF | 37/64 | 0.5781 | 14.68 | 65% | 14.5 mm |
| 3/4-10 | UNC | 21/32 | 0.6563 | 16.67 | 72% | 16.5 mm |
| 3/4-16 | UNF | 11/16 | 0.6875 | 17.46 | 77% | 17.5 mm |
| 7/8-9 | UNC | 49/64 | 0.7656 | 19.45 | 76% | 19.5 mm |
| 7/8-14 | UNF | 13/16 | 0.8125 | 20.64 | 67% | 20 mm |
| 1-8 | UNC | 7/8 | 0.8750 | 22.23 | 77% | 20 mm |
| 1-12 | UNF | 59/64 | 0.9219 | 23.42 | 72% | 20 mm |
% thread = TPI × (major diameter − drill diameter) ÷ 0.01299. See what percent of thread means.