Tap Drill Size – UNC

Below is a table of drill and tap sizes for Unified Screw Threads – Course, UNC.

UNC screws may not always be appropriate.  Depending on the application, you may be better off using UNF fasteners.


INCH SIZES – NATIONAL COARSE
TAP SIZE DRILL SIZE
#0-80 3/64″
#1-64 #53
#2-56 #51
#3-48 5/64″
#4-40 #43
#5-40 #39
#6-32 #36
#8-32 #29
#10-24 #25
#12-24 #17
1/4-20 #7
5/16-18 F
3/8-16 5/16
7/16-14 U
1/2-13 27/64
9/16-12 31/64
5/8-11 17/32
3/4-10 21/32
7/8-9 49/64
1″-8 7/8
1-1/8-7 63/64
1-1/4-7 1-7/64
1-1/2-6 1-11/32
1-3/4-5 1-35/64
2″-4-1/2 1-25/32

Metric Tap Drill Sizes
Standard UNF Tap Drill Sizes
Standard NPT Tap Drill Sizes

Unified Screw Threads – Fine (UNF)

Unified Screw Threads – Fine are the most common type of fine thread found in the US.  Fine threads are useful for imparting a higher tensile load to the bolt with lower assembly torque required.  Unified screw threads consist of a 60-degree thread profile.

The table below shows the major and minor diameters, thread pitch (given in threads per inch, tpi) and finally the diameter  area which is necessary for bolt tensile strength calculations.


Size Major Dia Threads Per Inch Pitch Dia Minor Dia External Minor Dia Internal Minor Dia Area Tensile Stress Area
# inch tpi inch inch inch sq. inch sq. inch
#0 0.06 80 0.0519 0.0451 0.0465 0.00151 0.0018
#1 0.073 72 0.064 0.0565 0.058 0.00237 0.00278
#2 0.086 64 0.0759 0.0674 0.0691 0.00339 0.00394
#3 0.099 56 0.0874 0.0778 0.0797 0.00451 0.00523
#4 0.112 48 0.0985 0.0871 0.0894 0.00566 0.00661
#5 0.125 44 0.1102 0.0979 0.1004 0.00716 0.0083
#6 0.138 40 0.1218 0.1082 0.1109 0.00874 0.01015
#8 0.164 36 0.146 0.1309 0.1339 0.01285 0.01474
#10 0.19 32 0.1697 0.1528 0.1562 0.0175 0.02
#12 0.216 28 0.1928 0.1734 0.1773 0.0226 0.0258
1/4 0.25 28 0.2268 0.2074 0.2113 0.0326 0.0364
5/16 0.3125 24 0.2854 0.2629 0.2674 0.0524 0.058
3/8 0.375 24 0.3479 0.3254 0.3299 0.0809 0.0878
7/16 0.4375 20 0.405 0.378 0.3834 0.109 0.1187
1/2 0.5 20 0.4675 0.4405 0.4459 0.1486 0.1599
9/16 0.5625 18 0.5264 0.4964 0.5024 0.189 0.203
5/8 0.625 18 0.5889 0.5589 0.5649 0.24 0.256
3/4 0.75 16 0.7094 0.6763 0.6823 0.351 0.373
7/8 0.875 14 0.8286 0.79 0.7977 0.48 0.509
1 1 12 0.9459 0.9001 0.9098 0.625 0.663
1-1/8 1.125 12 1.0709 1.0258 1.0348 0.812 0.856
1.25 12 1.1959 1.1508 1.1598 1.024 1.073
1-3/8 1.375 12 1.3209 1.2758 1.2848 1.26 1.315
1.5 12 1.4459 1.4008 1.4098 1.521 1.581

If you need a screw that is less sensitive to over-torquing, consider using a Unified Screw Thread – Course (UNC) instead of the Unified Screw Thread – Fine (UNF).

Unified Screw Threads – Course (UNC)

Unified Screw Threads – Course are the most common type of thread found in the US.  Unified screw threads consist of a 60-degree thread profile.

The table below shows the major and minor diameters, thread pitch (given in threads per inch, tpi) and finally the diameter  area which is necessary for bolt tensile strength calculations.


Size Major Dia Threads Per Inch Pitch Dia Minor Dia External Minor Dia Internal Minor Dia Area Tensile Stress Area
# inch tpi inch inch inch sq. inch sq. inch
#1 0.073 64 0.0629 0.0544 0.0561 0.00218 0.00263
#2 0.086 56 0.0744 0.0648 0.0667 0.0031 0.0037
#3 0.099 48 0.0855 0.0741 0.0764 0.00406 0.00487
#4 0.112 40 0.0958 0.0822 0.0849 0.00496 0.00604
#5 0.125 40 0.1088 0.0952 0.0979 0.00672 0.00796
#6 0.138 32 0.1177 0.1008 0.1042 0.00745 0.00909
#8 0.164 32 0.1437 0.1268 0.1302 0.01196 0.014
#10 0.19 24 0.1629 0.1404 0.1449 0.0145 0.0175
#12 0.216 24 0.1889 0.1664 0.1709 0.0206 0.0242
¼ 0.25 20 0.2175 0.1905 0.1959 0.0269 0.0318
5/16 0.3125 18 0.2764 0.2464 0.2524 0.0454 0.0524
3/8 0.375 16 0.3344 0.3005 0.3073 0.0678 0.0775
7/16 0.4375 14 0.3911 0.3525 0.3602 0.0933 0.1063
½ 0.5 13 0.45 0.4084 0.4167 0.1257 0.1419
9/16 0.5625 12 0.5084 0.4633 0.4723 0.162 0.182
5/8 0.625 11 0.566 0.5168 0.5266 0.202 0.226
¾ 0.75 10 0.685 0.6309 0.6417 0.302 0.334
7/8 0.875 9 0.8028 0.7427 0.7547 0.419 0.462
1 1 8 0.9188 0.8512 0.8647 0.551 0.606
1-1/8 1.125 7 1.0322 0.9549 0.9704 0.693 0.763
1.25 7 1.1572 1.0799 1.0954 0.89 0.969
1-3/8 1.375 6 1.2667 1.1766 1.1946 1.054 1.155
1.5 6 1.3917 1.3016 1.3196 1.294 1.405
1.75 5 1.6201 1.5119 1.5335 1.74 1.9
2 2 4.5 1.8557 1.7353 1.7594 2.3 2.5
2.25 4.5 2.1057 1.9853 2.0094 3.02 3.25
2.5 4 2.3376 2.2023 2.2294 3.72 4
2.75 4 2.5876 2.4523 2.4794 4.62 4.93
3 3 4 2.8376 2.7023 2.7294 5.62 5.97
3.25 4 3.0876 2.9523 2.9794 6.72 7.1
3.5 4 3.3376 3.2023 3.2294 7.92 8.33
3.75 4 3.5876 3.4523 3.4794 9.21 9.66
4 4 4 3.8376 3.7023 3.7294 10.61 11.08

If you need to apply more tensile load with less torque, consider using a Unified Screw Thread – Fine (UNF) instead of the Unified Screw Thread – Course (UNC).