Home - www.wermac.orgsearch wermac.org
www.wermac.org
bolts

Thread Pitch Chart

Thread series cover designations of diameter/pitch combinations that are measured by the number of threads per inch (TPI) applied to a single diameter.

Coarse Thread Series (UNC/UNRC) is the most common designation for general application bolts and nuts. Coarse thread is beneficial, because they are less likely to cross thread, more tolerant in adverse conditions and facilitate quick assembly.

Fine Thread Series (UNF/UNRF) is commonly used in precision applications. Because of the larger tensile stress areas, they have high tension strength. However, a longer engagement is required for fine thread applications than for coarse series threads to prevent stripping.

8-Thread Series (8UN) is the specified thread forming method for several ASTM standards including A193 B7, A193 B8/B8M, and A320. This series is used for diameters one inch and above.

Thread Pitch Chart
Coarse Thread Series - UNC
Nominal Size and Threads Per In. Basic Pitch Dia. Section at Minor Dia. Tensile Stress Area
In. Sq in. Sq in.
3/8 - 16 0.3344 0.0678 0.0775
7/16 - 14 0.3911 0.0933 0.1063
1/2 - 13 0.4500 0.1257 0.1419
9/16 - 12 0.5084 0.162 0.182
5/8 - 11 0.5660 0.202 0.226
3/4 - 10 0.6850 0.302 0.334
7/8 - 9 0.8028 0.419 0.462
1 - 8 0.9188 0.551 0.606
11/8 - 7 1.0322 0.693 0.763
11/4 - 7 1.1572 0.890 0.969
13/8 - 6 1.2667 1.054 1.155
11/2 - 6 1.3917 1.294 1.405
13/4 - 5 1.6201 1.74 1.90
2 - 41/2 1.8557 2.30 2.50
21/4 - 41/2 2.1057 3.02 3.25
21/2 - 4 2.3376 3.72 4.00
23/4 - 4 2.5876 4.62 4.93
3 - 4 2.8376 5.62 5.97
31/4 - 4 3.0876 6.72 7.10
31/2 - 4 3.3376 7.92 8.33
33/4 - 4 3.5876 9.21 9.66
4 - 4 3.8376 10.61 11.08
 
Fine Thread Series - UNF
Nominal Size and Threads Per In. Basic Pitch Dia. Section at Minor Dia. Tensile Stress Area
In. Sq in. Sq in.
3/8 - 24 0.3479 0.0809 0.0878
7/16 - 20 0.4050 0.1090 0.1187
1/2 - 20 0.4675 0.1486 0.1599
9/16 - 18 0.5264 0.189 0.203
5/8 - 18 0.5889 0.240 0.256
3/4 - 16 0.7094 0.351 0.373
7/8 - 14 0.8286 0.480 0.509
1 - 12 0.9459 0.625 0.663
11/8 - 12 1.0709 0.812 0.856
11/4 - 12 1.1959 1.024 1.073
13/8 - 12 1.3209 1.260 1.315
11/2 - 12 1.4459 1.521 1.581
 
8-Thread Series - 8UN
Nominal Size and Threads Per In. Basic Pitch Dia. Section at Minor Dia. Tensile Stress Area
In. Sq in. Sq in.
1 - 8 0.9188 0.551 0.606
11/8 - 8 1.0438 0.728 0.790
11/4 - 8 1.1688 0.929 1.000
13/8 - 8 1.2938 1.155 1.233
11/2 - 8 1.4188 1.405 1.492
15/8 - 8 1.5438 1.68 1.78
13/4 - 8 1.6688 1.98 2.08
17/8 - 8 1.7938 2.30 2.41
2 - 8 1.9188 2.65 2.77
21/4 - 8 2.1688 3.42 3.56
21/2 - 8 2.4188 4.29 4.44
23/4 - 8 2.6688 5.26 5.43
3 - 8 2.9188 6.32 6.51
31/4 - 8 3.1688 7.49 7.69
31/2 - 8 3.4188 8.75 8.96
33/4 - 8 3.6688 10.11 10.34
4 - 8 3.9188 11.57 11.81
Source: Portland Bolt & Mfg. Co.

Go to Top of Page