Tap Drill Chart
Interactive tap drill size chart for UNC, UNF, and metric threads. Find tap drill sizes for 50%, 65%, and 75% thread engagement. Searchable by thread designation.
Last updated April 2026
| Thread Size↑ | TPI↕ | Major Dia | Minor Dia | Pitch Dia | 50% Drill | 65% Drill | 75% Drill |
|---|---|---|---|---|---|---|---|
| #0-80 | 80 | 0.0600" | 0.0447" | 0.0519" | #54 (0.0550") | #55 (0.0520") | 3/64 (0.0469") |
| #1-64 | 64 | 0.0730" | 0.0538" | 0.0629" | #51 (0.0670") | #52 (0.0635") | #53 (0.0595") |
| #1-72 | 72 | 0.0730" | 0.0560" | 0.0640" | #51 (0.0670") | #52 (0.0635") | #53 (0.0595") |
| #2-56 | 56 | 0.0860" | 0.0641" | 0.0744" | #48 (0.0760") | #49 (0.0730") | #50 (0.0700") |
| #3-48 | 48 | 0.0990" | 0.0734" | 0.0855" | #43 (0.0890") | #44 (0.0860") | #47 (0.0785") |
| #4-40 | 40 | 0.1120" | 0.0813" | 0.0958" | 3/32 (0.0938") | #42 (0.0935") | #43 (0.0890") |
| #5-40 | 40 | 0.1250" | 0.0943" | 0.1088" | #35 (0.1100") | #36 (0.1065") | #38 (0.1015") |
| #6-32 | 32 | 0.1380" | 0.0997" | 0.1177" | #32 (0.1160") | #33 (0.1130") | #36 (0.1065") |
| #8-32 | 32 | 0.1640" | 0.1257" | 0.1437" | #27 (0.1440") | #28 (0.1405") | #29 (0.1360") |
| #10-24 | 24 | 0.1900" | 0.1389" | 0.1629" | #18 (0.1695") | #20 (0.1610") | #25 (0.1495") |
| #10-32 | 32 | 0.1900" | 0.1517" | 0.1697" | #16 (0.1770") | #19 (0.1660") | #21 (0.1590") |
| #12-24 | 24 | 0.2160" | 0.1649" | 0.1889" | #9 (0.1960") | #12 (0.1890") | #16 (0.1770") |
| 1/4"-20 | 20 | 0.2500" | 0.1887" | 0.2175" | 7/32 (0.2188") | #3 (0.2130") | #7 (0.2010") |
| 5/16"-18 | 18 | 0.3125" | 0.2443" | 0.2764" | 17/64 (0.2656") | G (0.2610") | F (0.2570") |
| 3/8"-16 | 16 | 0.3750" | 0.2983" | 0.3344" | S (0.3480") | Q (0.3320") | 5/16 (0.3125") |
| 7/16"-14 | 14 | 0.4375" | 0.3499" | 0.3911" | X (0.3970") | 25/64 (0.3906") | U (0.3680") |
| 1/2"-13 | 13 | 0.5000" | 0.4056" | 0.4500" | 15/32 (0.4688") | 29/64 (0.4531") | 27/64 (0.4219") |
| 9/16"-12 | 12 | 0.5625" | 0.4603" | 0.5084" | 17/32 (0.5313") | 33/64 (0.5156") | 31/64 (0.4844") |
| 5/8"-11 | 11 | 0.6250" | 0.5135" | 0.5660" | 37/64 (0.5781") | 9/16 (0.5625") | 17/32 (0.5313") |
| 3/4"-10 | 10 | 0.7500" | 0.6273" | 0.6850" | 45/64 (0.7031") | 11/16 (0.6875") | 21/32 (0.6563") |
| 7/8"-9 | 9 | 0.8750" | 0.7387" | 0.8028" | 53/64 (0.8281") | 51/64 (0.7969") | 49/64 (0.7656") |
| 1"-8 | 8 | 1.0000" | 0.8466" | 0.9188" | 61/64 (0.9531") | 59/64 (0.9219") | 7/8 (0.8750") |
| 1-1/8"-7 | 7 | 1.1250" | 0.9497" | 1.0322" | 1-3/64 (1.0469") | 1-1/64 (1.0156") | 63/64 (0.9844") |
| 1-1/4"-7 | 7 | 1.2500" | 1.0747" | 1.1572" | 1-11/64 (1.1719") | 1-9/64 (1.1406") | 1-7/64 (1.1094") |
| 1-1/2"-6 | 6 | 1.5000" | 1.2955" | 1.3917" | 1-27/64 (1.4219") | 1-25/64 (1.3906") | 1-11/32 (1.3438") |
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Frequently Asked Questions
What is a tap drill?
A tap drill is the drill size used to create a hole before tapping threads. The hole must be smaller than the thread major diameter to allow the tap to cut threads into the material.
What thread engagement should I use?
75% thread engagement is standard for most applications. Use 50-65% in hard materials or deep holes to reduce tap breakage risk. Full (100%) engagement is not practical and will break taps.
What is the tap drill size for 1/4-20?
The standard 75% thread engagement tap drill for 1/4-20 UNC is a #7 drill (0.201 inches).