Unified tap drill chart (UNC / UNF / UNEF)
Every ASME B1.1 standard-series thread from #0-80 to 1-1/2 in. Each drill is the nearest standard number, letter or fractional drill to the target, with the percent of thread it actually cuts. Form-tap drills are at 65% thread.
| Thread | 75% drill | 65% drill | 50% drill | Form tap (65%) | Minor dia (in) |
|---|---|---|---|---|---|
| #1-64 UNC | #53 0.0595 · 66.5% | #53 0.0595 · 66.5% | 1/16 0.0625 · 51.7% | #51 0.0670 | 0.0561 |
| #2-56 UNC | #50 0.0700 · 69% | #50 0.0700 · 69% | #49 0.0730 · 56% | 5/64 0.0781 | 0.0667 |
| #3-48 UNC | #47 0.0785 · 75.8% | #46 0.0810 · 66.5% | #44 0.0860 · 48% | #43 0.0890 | 0.0764 |
| #4-40 UNC | #43 0.0890 · 70.8% | #43 0.0890 · 70.8% | #41 0.0960 · 49.3% | #38 0.1015 | 0.0849 |
| #5-40 UNC | #38 0.1015 · 72.4% | #37 0.1040 · 64.7% | 7/64 0.1094 · 48.1% | #33 0.1130 | 0.0979 |
| #6-32 UNC | #36 0.1065 · 77.6% | #34 0.1110 · 66.5% | #32 0.1160 · 54.2% | 1/8 0.1250 | 0.1042 |
| #8-32 UNC | #29 0.1360 · 69% | #29 0.1360 · 69% | #27 0.1440 · 49.3% | #25 0.1495 | 0.1302 |
| #10-24 UNC | #25 0.1495 · 74.8% | #23 0.1540 · 66.5% | #20 0.1610 · 53.6% | 11/64 0.1719 | 0.1449 |
| #12-24 UNC | #16 0.1770 · 72.1% | #15 0.1800 · 66.5% | #12 0.1890 · 49.9% | #8 0.1990 | 0.1709 |
| 1/4-20 UNC | #7 0.2010 · 75.4% | #4 0.2090 · 63.1% | 7/32 0.2188 · 48.1% | #1 0.2280 | 0.1959 |
| 5/16-18 UNC | F 0.2570 · 76.9% | 17/64 0.2656 · 65% | J 0.2770 · 49.2% | L 0.2900 | 0.2524 |
| 3/8-16 UNC | 5/16 0.3125 · 77% | P 0.3230 · 64% | Q 0.3320 · 53% | S 0.3480 | 0.3073 |
| 7/16-14 UNC | U 0.3680 · 74.9% | V 0.3770 · 65.2% | 25/64 0.3906 · 50.5% | 13/32 0.4063 | 0.3602 |
| 1/2-13 UNC | 27/64 0.4219 · 78.2% | 7/16 0.4375 · 62.5% | 29/64 0.4531 · 46.9% | 15/32 0.4688 | 0.4167 |
| 9/16-12 UNC | 31/64 0.4844 · 72.2% | 31/64 0.4844 · 72.2% | 33/64 0.5156 · 43.3% | 17/32 0.5313 | 0.4723 |
| 5/8-11 UNC | 17/32 0.5313 · 79.4% | 35/64 0.5469 · 66.2% | 9/16 0.5625 · 52.9% | 37/64 0.5781 | 0.5266 |
| 3/4-10 UNC | 21/32 0.6563 · 72.2% | 43/64 0.6719 · 60.1% | 11/16 0.6875 · 48.1% | 45/64 0.7031 | 0.6417 |
| 7/8-9 UNC | 49/64 0.7656 · 75.8% | 25/32 0.7813 · 65% | 51/64 0.7969 · 54.1% | 53/64 0.8281 | 0.7547 |
| 1-8 UNC | 7/8 0.8750 · 77% | 57/64 0.8906 · 67.4% | 59/64 0.9219 · 48.1% | 15/16 0.9375 | 0.8647 |
| 1-1/8-7 UNC | 63/64 0.9844 · 75.8% | 1 1.0000 · 67.4% | 1-1/32 1.0313 · 50.5% | 1-1/16 1.0625 | 0.9704 |
| 1-1/4-7 UNC | 1-7/64 1.1094 · 75.8% | 1-1/8 1.1250 · 67.4% | 1-5/32 1.1563 · 50.5% | 1-3/16 1.1875 | 1.0954 |
| 1-3/8-6 UNC | 1-7/32 1.2188 · 72.2% | 1-15/64 1.2344 · 65% | 1-17/64 1.2656 · 50.5% | 1-19/64 1.2969 | 1.1946 |
| 1-1/2-6 UNC | 1-11/32 1.3438 · 72.2% | 1-23/64 1.3594 · 65% | 1-25/64 1.3906 · 50.5% | 1-27/64 1.4219 | 1.3196 |
| 1-3/4-5 UNC | 1-9/16 1.5625 · 72.2% | 1-37/64 1.5781 · 66.2% | 1-5/8 1.6250 · 48.1% | 1-21/32 1.6563 | 1.5335 |
| 2-4.5 UNC | 1-25/32 1.7813 · 75.8% | 1-13/16 1.8125 · 65% | 1-55/64 1.8594 · 48.7% | 1-29/32 1.9063 | 1.7594 |
| 2-1/4-4.5 UNC | 2-1/32 2.0313 · 75.8% | 2-1/16 2.0625 · 65% | 2-7/64 2.1094 · 48.7% | 2-5/32 2.1563 | 2.0094 |
| 2-1/2-4 UNC | 2-1/4 2.2500 · 77% | 2-9/32 2.2813 · 67.4% | 2-11/32 2.3438 · 48.1% | 2-3/8 2.3750 | 2.2294 |
| 2-3/4-4 UNC | 2-1/2 2.5000 · 77% | 2-17/32 2.5313 · 67.4% | 2-19/32 2.5938 · 48.1% | 2-5/8 2.6250 | 2.4794 |
| 3-4 UNC | 2-3/4 2.7500 · 77% | 2-25/32 2.7813 · 67.4% | 2-27/32 2.8438 · 48.1% | 2-7/8 2.8750 | 2.7294 |
| 3-1/4-4 UNC | 3 3.0000 · 77% | 3-1/16 3.0625 · 57.7% | 3-1/16 3.0625 · 57.7% | 3-1/8 3.1250 | 2.9794 |
| 3-1/2-4 UNC | 3-1/4 3.2500 · 77% | 3-5/16 3.3125 · 57.7% | 3-5/16 3.3125 · 57.7% | 3-3/8 3.3750 | 3.2294 |
| 3-3/4-4 UNC | 3-1/2 3.5000 · 77% | 3-9/16 3.5625 · 57.7% | 3-9/16 3.5625 · 57.7% | 3-5/8 3.6250 | 3.4794 |
| 4-4 UNC | 3-3/4 3.7500 · 77% | 3-13/16 3.8125 · 57.7% | 3-13/16 3.8125 · 57.7% | 3-7/8 3.8750 | 3.7294 |
| Thread | 75% drill | 65% drill | 50% drill | Form tap (65%) | Minor dia (in) |
|---|---|---|---|---|---|
| #0-80 UNF | 3/64 0.0469 · 80.8% | #55 0.0520 · 49.3% | #55 0.0520 · 49.3% | #54 0.0550 | 0.0465 |
| #1-72 UNF | #53 0.0595 · 74.8% | 1/16 0.0625 · 58.2% | #52 0.0635 · 52.7% | #51 0.0670 | 0.0580 |
| #2-64 UNF | #50 0.0700 · 78.8% | #49 0.0730 · 64% | #48 0.0760 · 49.3% | #47 0.0785 | 0.0691 |
| #3-56 UNF | #45 0.0820 · 73.3% | #45 0.0820 · 73.3% | #44 0.0860 · 56% | #43 0.0890 | 0.0797 |
| #4-48 UNF | #42 0.0935 · 68.4% | 3/32 0.0938 · 67.4% | #40 0.0980 · 51.7% | #37 0.1040 | 0.0894 |
| #5-44 UNF | #37 0.1040 · 71.1% | #36 0.1065 · 62.7% | #35 0.1100 · 50.8% | #32 0.1160 | 0.1004 |
| #6-40 UNF | #33 0.1130 · 77% | #32 0.1160 · 67.7% | #31 0.1200 · 55.4% | #30 0.1285 | 0.1109 |
| #8-36 UNF | #29 0.1360 · 77.6% | #28 0.1405 · 65.1% | #26 0.1470 · 47.1% | #24 0.1520 | 0.1339 |
| #10-32 UNF | #21 0.1590 · 76.4% | #19 0.1660 · 59.1% | #18 0.1695 · 50.5% | #16 0.1770 | 0.1562 |
| #12-28 UNF | #14 0.1820 · 73.3% | #13 0.1850 · 66.8% | #10 0.1935 · 48.5% | #7 0.2010 | 0.1773 |
| 1/4-28 UNF | #3 0.2130 · 79.8% | 7/32 0.2188 · 67.4% | #1 0.2280 · 47.4% | 15/64 0.2344 | 0.2113 |
| 5/16-24 UNF | I 0.2720 · 74.8% | J 0.2770 · 65.6% | 9/32 0.2813 · 57.7% | M 0.2950 | 0.2674 |
| 3/8-24 UNF | Q 0.3320 · 79.4% | R 0.3390 · 66.5% | S 0.3480 · 49.9% | T 0.3580 | 0.3299 |
| 7/16-20 UNF | 25/64 0.3906 · 72.2% | X 0.3970 · 62.4% | Y 0.4040 · 51.6% | Z 0.4130 | 0.3834 |
| 1/2-20 UNF | 29/64 0.4531 · 72.2% | 29/64 0.4531 · 72.2% | 15/32 0.4688 · 48.1% | 31/64 0.4844 | 0.4459 |
| 9/16-18 UNF | 33/64 0.5156 · 65% | 33/64 0.5156 · 65% | 17/32 0.5313 · 43.3% | 17/32 0.5313 | 0.5024 |
| 5/8-18 UNF | 37/64 0.5781 · 65% | 37/64 0.5781 · 65% | 19/32 0.5938 · 43.3% | 19/32 0.5938 | 0.5649 |
| 3/4-16 UNF | 11/16 0.6875 · 77% | 45/64 0.7031 · 57.7% | 45/64 0.7031 · 57.7% | 23/32 0.7188 | 0.6823 |
| 7/8-14 UNF | 13/16 0.8125 · 67.4% | 13/16 0.8125 · 67.4% | 53/64 0.8281 · 50.5% | 27/32 0.8438 | 0.7977 |
| 1-12 UNF | 59/64 0.9219 · 72.2% | 59/64 0.9219 · 72.2% | 61/64 0.9531 · 43.3% | 31/32 0.9688 | 0.9098 |
| 1-1/8-12 UNF | 1-3/64 1.0469 · 72.2% | 1-3/64 1.0469 · 72.2% | 1-5/64 1.0781 · 43.3% | 1-3/32 1.0938 | 1.0348 |
| 1-1/4-12 UNF | 1-11/64 1.1719 · 72.2% | 1-11/64 1.1719 · 72.2% | 1-13/64 1.2031 · 43.3% | 1-7/32 1.2188 | 1.1598 |
| 1-3/8-12 UNF | 1-19/64 1.2969 · 72.2% | 1-19/64 1.2969 · 72.2% | 1-21/64 1.3281 · 43.3% | 1-11/32 1.3438 | 1.2848 |
| 1-1/2-12 UNF | 1-27/64 1.4219 · 72.2% | 1-27/64 1.4219 · 72.2% | 1-29/64 1.4531 · 43.3% | 1-15/32 1.4688 | 1.4098 |
| Thread | 75% drill | 65% drill | 50% drill | Form tap (65%) | Minor dia (in) |
|---|---|---|---|---|---|
| #12-32 UNEF | #13 0.1850 · 76.4% | #12 0.1890 · 66.5% | #9 0.1960 · 49.3% | 13/64 0.2031 | 0.1822 |
| 1/4-32 UNEF | 7/32 0.2188 · 77% | #2 0.2210 · 71.4% | #1 0.2280 · 54.2% | 15/64 0.2344 | 0.2162 |
| 5/16-32 UNEF | 9/32 0.2813 · 77% | L 0.2900 · 55.4% | L 0.2900 · 55.4% | 19/64 0.2969 | 0.2787 |
| 3/8-32 UNEF | 11/32 0.3438 · 77% | S 0.3480 · 66.5% | T 0.3580 · 41.9% | 23/64 0.3594 | 0.3412 |
| 7/16-28 UNEF | Y 0.4040 · 72.2% | 13/32 0.4063 · 67.4% | Z 0.4130 · 52.8% | 27/64 0.4219 | 0.3988 |
| 1/2-28 UNEF | 15/32 0.4688 · 67.4% | 15/32 0.4688 · 67.4% | 31/64 0.4844 · 33.7% | 31/64 0.4844 | 0.4613 |
| 9/16-24 UNEF | 33/64 0.5156 · 86.6% | 17/32 0.5313 · 57.7% | 17/32 0.5313 · 57.7% | 35/64 0.5469 | 0.5174 |
| 5/8-24 UNEF | 37/64 0.5781 · 86.6% | 19/32 0.5938 · 57.7% | 19/32 0.5938 · 57.7% | 39/64 0.6094 | 0.5799 |
| 11/16-24 UNEF | 41/64 0.6406 · 86.6% | 21/32 0.6563 · 57.7% | 21/32 0.6563 · 57.7% | 43/64 0.6719 | 0.6424 |
| 3/4-20 UNEF | 45/64 0.7031 · 72.2% | 45/64 0.7031 · 72.2% | 23/32 0.7188 · 48.1% | 47/64 0.7344 | 0.6959 |
| 13/16-20 UNEF | 49/64 0.7656 · 72.2% | 49/64 0.7656 · 72.2% | 25/32 0.7813 · 48.1% | 51/64 0.7969 | 0.7584 |
| 7/8-20 UNEF | 53/64 0.8281 · 72.2% | 53/64 0.8281 · 72.2% | 27/32 0.8438 · 48.1% | 55/64 0.8594 | 0.8209 |
| 15/16-20 UNEF | 57/64 0.8906 · 72.2% | 57/64 0.8906 · 72.2% | 29/32 0.9063 · 48.1% | 59/64 0.9219 | 0.8834 |
| 1-20 UNEF | 61/64 0.9531 · 72.2% | 61/64 0.9531 · 72.2% | 31/32 0.9688 · 48.1% | 63/64 0.9844 | 0.9459 |
| 1-1/16-18 UNEF | 1-1/64 1.0156 · 65% | 1-1/64 1.0156 · 65% | 1-1/32 1.0313 · 43.3% | 1-1/32 1.0313 | 1.0024 |
| 1-1/8-18 UNEF | 1-5/64 1.0781 · 65% | 1-5/64 1.0781 · 65% | 1-3/32 1.0938 · 43.3% | 1-3/32 1.0938 | 1.0649 |
| 1-3/16-18 UNEF | 1-9/64 1.1406 · 65% | 1-9/64 1.1406 · 65% | 1-5/32 1.1563 · 43.3% | 1-5/32 1.1563 | 1.1274 |
| 1-1/4-18 UNEF | 1-13/64 1.2031 · 65% | 1-13/64 1.2031 · 65% | 1-7/32 1.2188 · 43.3% | 1-7/32 1.2188 | 1.1899 |
| 1-5/16-18 UNEF | 1-17/64 1.2656 · 65% | 1-17/64 1.2656 · 65% | 1-9/32 1.2813 · 43.3% | 1-9/32 1.2813 | 1.2524 |
| 1-3/8-18 UNEF | 1-21/64 1.3281 · 65% | 1-21/64 1.3281 · 65% | 1-11/32 1.3438 · 43.3% | 1-11/32 1.3438 | 1.3149 |
| 1-7/16-18 UNEF | 1-25/64 1.3906 · 65% | 1-25/64 1.3906 · 65% | 1-13/32 1.4063 · 43.3% | 1-13/32 1.4063 | 1.3774 |
| 1-1/2-18 UNEF | 1-29/64 1.4531 · 65% | 1-29/64 1.4531 · 65% | 1-15/32 1.4688 · 43.3% | 1-15/32 1.4688 | 1.4399 |
| 1-9/16-18 UNEF | 1-33/64 1.5156 · 65% | 1-33/64 1.5156 · 65% | 1-17/32 1.5313 · 43.3% | 1-17/32 1.5313 | 1.5024 |
| 1-5/8-18 UNEF | 1-37/64 1.5781 · 65% | 1-37/64 1.5781 · 65% | 1-19/32 1.5938 · 43.3% | 1-19/32 1.5938 | 1.5649 |
| 1-11/16-18 UNEF | 1-41/64 1.6406 · 65% | 1-41/64 1.6406 · 65% | 1-21/32 1.6563 · 43.3% | 1-21/32 1.6563 | 1.6274 |
Common questions
- How is percent of thread calculated?
- % thread = threads per inch × (major diameter − drill) ÷ 0.01299 (Machinery's Handbook). A #7 drill in 1/4-20 gives about 75%.
- When should I use 50% or 65% thread?
- Tough or work-hardening material, deep holes and small taps: less thread means much lower tap torque for little loss of strength.
- What drill for a 1-12 UNF tap?
- 59/64 in gives about 72% thread. Some charts list 15/16 in, which gives only about 58%.
Calculators that use this data
Tap Drill & Thread % CalculatorPercent of thread for any drill (cut and form taps), 75 / 65 / 50% tap drills, UNC / UNF / metric chart with thread limits, every thread to 4 in and M64, pipe taps and STI / Helicoil.Drill Chart & Size FinderNearest-drill finder over the full drill chart (#97-#1, A-Z, 1/64-4 in, 0.1-60 mm), drill speeds and pecks, Silver & Deming, aircraft and center drills, counterbores and reamer pre-drills.
More reference charts
Free for machinists & programmers
Put your skills on a free talent profile
Machines, controls, certs and saved calculations in one profile shops can find.
Create free profile For your shop
Bring shift handoffs to your shop
Stop losing job status between shifts. Every station's notes, counts and issues, handed off cleanly.
See shift handoffs