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.

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    UNC (coarse) tap drills
    Thread75% drill65% drill50% drillForm 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 0.06700.0561
    #2-56 UNC#50 0.0700 · 69%#50 0.0700 · 69%#49 0.0730 · 56%5/64 0.07810.0667
    #3-48 UNC#47 0.0785 · 75.8%#46 0.0810 · 66.5%#44 0.0860 · 48%#43 0.08900.0764
    #4-40 UNC#43 0.0890 · 70.8%#43 0.0890 · 70.8%#41 0.0960 · 49.3%#38 0.10150.0849
    #5-40 UNC#38 0.1015 · 72.4%#37 0.1040 · 64.7%7/64 0.1094 · 48.1%#33 0.11300.0979
    #6-32 UNC#36 0.1065 · 77.6%#34 0.1110 · 66.5%#32 0.1160 · 54.2%1/8 0.12500.1042
    #8-32 UNC#29 0.1360 · 69%#29 0.1360 · 69%#27 0.1440 · 49.3%#25 0.14950.1302
    #10-24 UNC#25 0.1495 · 74.8%#23 0.1540 · 66.5%#20 0.1610 · 53.6%11/64 0.17190.1449
    #12-24 UNC#16 0.1770 · 72.1%#15 0.1800 · 66.5%#12 0.1890 · 49.9%#8 0.19900.1709
    1/4-20 UNC#7 0.2010 · 75.4%#4 0.2090 · 63.1%7/32 0.2188 · 48.1%#1 0.22800.1959
    5/16-18 UNCF 0.2570 · 76.9%17/64 0.2656 · 65%J 0.2770 · 49.2%L 0.29000.2524
    3/8-16 UNC5/16 0.3125 · 77%P 0.3230 · 64%Q 0.3320 · 53%S 0.34800.3073
    7/16-14 UNCU 0.3680 · 74.9%V 0.3770 · 65.2%25/64 0.3906 · 50.5%13/32 0.40630.3602
    1/2-13 UNC27/64 0.4219 · 78.2%7/16 0.4375 · 62.5%29/64 0.4531 · 46.9%15/32 0.46880.4167
    9/16-12 UNC31/64 0.4844 · 72.2%31/64 0.4844 · 72.2%33/64 0.5156 · 43.3%17/32 0.53130.4723
    5/8-11 UNC17/32 0.5313 · 79.4%35/64 0.5469 · 66.2%9/16 0.5625 · 52.9%37/64 0.57810.5266
    3/4-10 UNC21/32 0.6563 · 72.2%43/64 0.6719 · 60.1%11/16 0.6875 · 48.1%45/64 0.70310.6417
    7/8-9 UNC49/64 0.7656 · 75.8%25/32 0.7813 · 65%51/64 0.7969 · 54.1%53/64 0.82810.7547
    1-8 UNC7/8 0.8750 · 77%57/64 0.8906 · 67.4%59/64 0.9219 · 48.1%15/16 0.93750.8647
    1-1/8-7 UNC63/64 0.9844 · 75.8%1 1.0000 · 67.4%1-1/32 1.0313 · 50.5%1-1/16 1.06250.9704
    1-1/4-7 UNC1-7/64 1.1094 · 75.8%1-1/8 1.1250 · 67.4%1-5/32 1.1563 · 50.5%1-3/16 1.18751.0954
    1-3/8-6 UNC1-7/32 1.2188 · 72.2%1-15/64 1.2344 · 65%1-17/64 1.2656 · 50.5%1-19/64 1.29691.1946
    1-1/2-6 UNC1-11/32 1.3438 · 72.2%1-23/64 1.3594 · 65%1-25/64 1.3906 · 50.5%1-27/64 1.42191.3196
    1-3/4-5 UNC1-9/16 1.5625 · 72.2%1-37/64 1.5781 · 66.2%1-5/8 1.6250 · 48.1%1-21/32 1.65631.5335
    2-4.5 UNC1-25/32 1.7813 · 75.8%1-13/16 1.8125 · 65%1-55/64 1.8594 · 48.7%1-29/32 1.90631.7594
    2-1/4-4.5 UNC2-1/32 2.0313 · 75.8%2-1/16 2.0625 · 65%2-7/64 2.1094 · 48.7%2-5/32 2.15632.0094
    2-1/2-4 UNC2-1/4 2.2500 · 77%2-9/32 2.2813 · 67.4%2-11/32 2.3438 · 48.1%2-3/8 2.37502.2294
    2-3/4-4 UNC2-1/2 2.5000 · 77%2-17/32 2.5313 · 67.4%2-19/32 2.5938 · 48.1%2-5/8 2.62502.4794
    3-4 UNC2-3/4 2.7500 · 77%2-25/32 2.7813 · 67.4%2-27/32 2.8438 · 48.1%2-7/8 2.87502.7294
    3-1/4-4 UNC3 3.0000 · 77%3-1/16 3.0625 · 57.7%3-1/16 3.0625 · 57.7%3-1/8 3.12502.9794
    3-1/2-4 UNC3-1/4 3.2500 · 77%3-5/16 3.3125 · 57.7%3-5/16 3.3125 · 57.7%3-3/8 3.37503.2294
    3-3/4-4 UNC3-1/2 3.5000 · 77%3-9/16 3.5625 · 57.7%3-9/16 3.5625 · 57.7%3-5/8 3.62503.4794
    4-4 UNC3-3/4 3.7500 · 77%3-13/16 3.8125 · 57.7%3-13/16 3.8125 · 57.7%3-7/8 3.87503.7294
    UNF (fine) tap drills
    Thread75% drill65% drill50% drillForm tap (65%)Minor dia (in)
    #0-80 UNF3/64 0.0469 · 80.8%#55 0.0520 · 49.3%#55 0.0520 · 49.3%#54 0.05500.0465
    #1-72 UNF#53 0.0595 · 74.8%1/16 0.0625 · 58.2%#52 0.0635 · 52.7%#51 0.06700.0580
    #2-64 UNF#50 0.0700 · 78.8%#49 0.0730 · 64%#48 0.0760 · 49.3%#47 0.07850.0691
    #3-56 UNF#45 0.0820 · 73.3%#45 0.0820 · 73.3%#44 0.0860 · 56%#43 0.08900.0797
    #4-48 UNF#42 0.0935 · 68.4%3/32 0.0938 · 67.4%#40 0.0980 · 51.7%#37 0.10400.0894
    #5-44 UNF#37 0.1040 · 71.1%#36 0.1065 · 62.7%#35 0.1100 · 50.8%#32 0.11600.1004
    #6-40 UNF#33 0.1130 · 77%#32 0.1160 · 67.7%#31 0.1200 · 55.4%#30 0.12850.1109
    #8-36 UNF#29 0.1360 · 77.6%#28 0.1405 · 65.1%#26 0.1470 · 47.1%#24 0.15200.1339
    #10-32 UNF#21 0.1590 · 76.4%#19 0.1660 · 59.1%#18 0.1695 · 50.5%#16 0.17700.1562
    #12-28 UNF#14 0.1820 · 73.3%#13 0.1850 · 66.8%#10 0.1935 · 48.5%#7 0.20100.1773
    1/4-28 UNF#3 0.2130 · 79.8%7/32 0.2188 · 67.4%#1 0.2280 · 47.4%15/64 0.23440.2113
    5/16-24 UNFI 0.2720 · 74.8%J 0.2770 · 65.6%9/32 0.2813 · 57.7%M 0.29500.2674
    3/8-24 UNFQ 0.3320 · 79.4%R 0.3390 · 66.5%S 0.3480 · 49.9%T 0.35800.3299
    7/16-20 UNF25/64 0.3906 · 72.2%X 0.3970 · 62.4%Y 0.4040 · 51.6%Z 0.41300.3834
    1/2-20 UNF29/64 0.4531 · 72.2%29/64 0.4531 · 72.2%15/32 0.4688 · 48.1%31/64 0.48440.4459
    9/16-18 UNF33/64 0.5156 · 65%33/64 0.5156 · 65%17/32 0.5313 · 43.3%17/32 0.53130.5024
    5/8-18 UNF37/64 0.5781 · 65%37/64 0.5781 · 65%19/32 0.5938 · 43.3%19/32 0.59380.5649
    3/4-16 UNF11/16 0.6875 · 77%45/64 0.7031 · 57.7%45/64 0.7031 · 57.7%23/32 0.71880.6823
    7/8-14 UNF13/16 0.8125 · 67.4%13/16 0.8125 · 67.4%53/64 0.8281 · 50.5%27/32 0.84380.7977
    1-12 UNF59/64 0.9219 · 72.2%59/64 0.9219 · 72.2%61/64 0.9531 · 43.3%31/32 0.96880.9098
    1-1/8-12 UNF1-3/64 1.0469 · 72.2%1-3/64 1.0469 · 72.2%1-5/64 1.0781 · 43.3%1-3/32 1.09381.0348
    1-1/4-12 UNF1-11/64 1.1719 · 72.2%1-11/64 1.1719 · 72.2%1-13/64 1.2031 · 43.3%1-7/32 1.21881.1598
    1-3/8-12 UNF1-19/64 1.2969 · 72.2%1-19/64 1.2969 · 72.2%1-21/64 1.3281 · 43.3%1-11/32 1.34381.2848
    1-1/2-12 UNF1-27/64 1.4219 · 72.2%1-27/64 1.4219 · 72.2%1-29/64 1.4531 · 43.3%1-15/32 1.46881.4098
    UNEF (extra fine) tap drills
    Thread75% drill65% drill50% drillForm 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 0.20310.1822
    1/4-32 UNEF7/32 0.2188 · 77%#2 0.2210 · 71.4%#1 0.2280 · 54.2%15/64 0.23440.2162
    5/16-32 UNEF9/32 0.2813 · 77%L 0.2900 · 55.4%L 0.2900 · 55.4%19/64 0.29690.2787
    3/8-32 UNEF11/32 0.3438 · 77%S 0.3480 · 66.5%T 0.3580 · 41.9%23/64 0.35940.3412
    7/16-28 UNEFY 0.4040 · 72.2%13/32 0.4063 · 67.4%Z 0.4130 · 52.8%27/64 0.42190.3988
    1/2-28 UNEF15/32 0.4688 · 67.4%15/32 0.4688 · 67.4%31/64 0.4844 · 33.7%31/64 0.48440.4613
    9/16-24 UNEF33/64 0.5156 · 86.6%17/32 0.5313 · 57.7%17/32 0.5313 · 57.7%35/64 0.54690.5174
    5/8-24 UNEF37/64 0.5781 · 86.6%19/32 0.5938 · 57.7%19/32 0.5938 · 57.7%39/64 0.60940.5799
    11/16-24 UNEF41/64 0.6406 · 86.6%21/32 0.6563 · 57.7%21/32 0.6563 · 57.7%43/64 0.67190.6424
    3/4-20 UNEF45/64 0.7031 · 72.2%45/64 0.7031 · 72.2%23/32 0.7188 · 48.1%47/64 0.73440.6959
    13/16-20 UNEF49/64 0.7656 · 72.2%49/64 0.7656 · 72.2%25/32 0.7813 · 48.1%51/64 0.79690.7584
    7/8-20 UNEF53/64 0.8281 · 72.2%53/64 0.8281 · 72.2%27/32 0.8438 · 48.1%55/64 0.85940.8209
    15/16-20 UNEF57/64 0.8906 · 72.2%57/64 0.8906 · 72.2%29/32 0.9063 · 48.1%59/64 0.92190.8834
    1-20 UNEF61/64 0.9531 · 72.2%61/64 0.9531 · 72.2%31/32 0.9688 · 48.1%63/64 0.98440.9459
    1-1/16-18 UNEF1-1/64 1.0156 · 65%1-1/64 1.0156 · 65%1-1/32 1.0313 · 43.3%1-1/32 1.03131.0024
    1-1/8-18 UNEF1-5/64 1.0781 · 65%1-5/64 1.0781 · 65%1-3/32 1.0938 · 43.3%1-3/32 1.09381.0649
    1-3/16-18 UNEF1-9/64 1.1406 · 65%1-9/64 1.1406 · 65%1-5/32 1.1563 · 43.3%1-5/32 1.15631.1274
    1-1/4-18 UNEF1-13/64 1.2031 · 65%1-13/64 1.2031 · 65%1-7/32 1.2188 · 43.3%1-7/32 1.21881.1899
    1-5/16-18 UNEF1-17/64 1.2656 · 65%1-17/64 1.2656 · 65%1-9/32 1.2813 · 43.3%1-9/32 1.28131.2524
    1-3/8-18 UNEF1-21/64 1.3281 · 65%1-21/64 1.3281 · 65%1-11/32 1.3438 · 43.3%1-11/32 1.34381.3149
    1-7/16-18 UNEF1-25/64 1.3906 · 65%1-25/64 1.3906 · 65%1-13/32 1.4063 · 43.3%1-13/32 1.40631.3774
    1-1/2-18 UNEF1-29/64 1.4531 · 65%1-29/64 1.4531 · 65%1-15/32 1.4688 · 43.3%1-15/32 1.46881.4399
    1-9/16-18 UNEF1-33/64 1.5156 · 65%1-33/64 1.5156 · 65%1-17/32 1.5313 · 43.3%1-17/32 1.53131.5024
    1-5/8-18 UNEF1-37/64 1.5781 · 65%1-37/64 1.5781 · 65%1-19/32 1.5938 · 43.3%1-19/32 1.59381.5649
    1-11/16-18 UNEF1-41/64 1.6406 · 65%1-41/64 1.6406 · 65%1-21/32 1.6563 · 43.3%1-21/32 1.65631.6274

    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

    Thread Percentage CalculatorPercent of thread from any drill for cut and form taps, with 75%, 65% and 50% tap drills.Tap Drill ChartRecommended tap drill sizes for UNC, UNF, and metric threads.Drill Chart & Size FinderFractional, number, letter and metric drills with decimal equivalents and a nearest-drill finder.

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