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 |
1¼ |
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 |
1½ |
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).