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28UN - 60 Degree Unified Threads

The 28 thread series (28-UN) have been used more or less widely in industry for various applications where the Standard Coarse, Fine or Extra-fine Series were not as applicable. They are now recognized as Standard Unified Thread Series in a specified selection of diameters for each pitch.

5/16" - 1" 1 1/16" - 1 1/2"

28UN Threads

Nominal Size External (b) Internal (b)
Threads per Inch and Series Designation Class Allowance Major Diameter Minor Diameter UNR Minor Dia.,c Max (Ref.) Class Minor Diameter Pitch Diameter Major Diameter
Max (d) Min Min (e) Max (d) Min Min Max Min Max Min
5/16" - 28UN 2A 0.001 7.912 7.747 - 7.323 7.236 6.83 2B 6.96 7.163 7.348 7.46 7.938
5/16" - 28UN 3A 0 7.938 7.772 - 7.348 7.282 6.855 3B 6.96 7.13 7.348 7.432 7.938
3/8" - 28UN 2A 0.0011 9.497 9.332 - 8.908 8.816 8.415 2B 8.534 8.763 8.936 9.053 9.525
3/8" - 28UN 3A 0 9.525 9.36 - 8.936 8.867 8.443 3B 8.534 8.702 8.936 9.025 9.525
9/16" - 28UN 2A 0.0011 14.26 14.094 - 13.67 13.576 13.178 2B 13.31 13.513 13.698 13.82 14.288
9/16" - 28UN 3A 0 14.288 14.122 - 13.698 13.627 13.205 3B 13.31 13.465 13.698 13.79 14.288
5/8" - 28UN 2A 0.0011 15.847 15.682 - 15.258 15.161 14.765 2B 14.884 15.113 15.286 15.41 15.875
5/8" - 28UN 3A 0 15.875 15.71 - 15.286 15.215 14.793 3B 14.884 15.052 15.286 15.38 15.875
11/16" - 28UN 2A 0.0011 17.435 17.269 - 16.845 16.749 16.353 2B 16.485 16.688 16.873 16.998 17.463
11/16" - 28UN 3A 0 17.463 17.297 - 16.873 16.802 16.38 3B 16.485 16.64 16.873 16.967 17.463
3/4" - 28UN 2A 0.0012 19.02 18.854 - 18.43 18.334 17.937 2B 18.059 18.288 18.461 18.588 19.05
3/4" - 28UN 3A 0 19.05 18.885 - 18.461 18.387 17.968 3B 18.059 18.227 18.461 18.555 19.05
13/16" - 28UN 2A 0.0012 20.607 20.442 - 20.018 19.921 19.525 2B 19.66 19.863 20.048 20.175 20.638
13/16" - 28UN 3A 0 20.638 20.472 - 20.048 19.975 19.555 3B 19.66 19.815 20.048 20.142 20.638
7/8" - 28UN 2A 0.0012 22.195 22.029 - 21.605 21.509 21.112 2B 21.234 21.463 21.636 21.763 22.225
7/8" - 28UN 3A 0 22.225 22.06 - 21.636 21.562 21.143 3B 21.234 21.402 21.636 21.73 22.225
15/16" - 28UN 2A 0.0012 23.782 23.617 - 23.193 23.091 22.7 2B 22.835 23.038 23.223 23.355 23.813
15/16" - 28UN 3A 0 23.813 23.647 - 23.223 23.147 22.73 3B 22.835 22.99 23.223 23.322 23.813
1 3/8" - 28UN 3A 0 34.925 34.544 - 32.863 32.725 31.145 3B 31.496 31.869 32.863 33.04 34.925
1" - 28UN 2A 0.0012 25.37 25.204 - 24.78 24.679 24.287 2B 24.409 24.638 24.811 24.943 25.4
1" - 28UN 3A 0 25.4 25.235 - 24.811 24.735 24.318 3B 24.409 24.577 24.811 24.91 25.4
1 1/16" - 28UN 2A 0.0012 26.957 26.792 - 26.368 26.266 25.875 2B 26.01 26.213 26.398 26.53 26.988
1 1/16" - 28UN 3A 0 26.988 26.822 - 26.398 26.322 25.905 3B 26.01 26.165 26.398 26.497 26.988
1 1/8" - 28UN 2A 0.0012 28.545 28.379 - 27.955 27.854 27.462 2B 27.584 27.813 27.986 28.118 28.575
1 1/8" - 28UN 3A 0 28.575 28.41 - 27.986 27.91 27.493 3B 27.584 27.752 27.986 28.085 28.575
1 3/8" - 28UN 2A 0.0012 30.132 29.967 - 29.543 29.439 29.05 2B 29.185 29.388 29.573 29.708 30.163
1 3/8" - 28UN 3A 0 30.163 29.997 - 29.573 29.494 29.08 3B 29.185 29.34 29.573 29.675 30.163
1 1/4" - 28UN 2A 0.0012 31.72 31.554 - 31.13 31.026 30.637 2B 30.759 30.988 31.161 31.295 31.75
1 1/4" - 28UN 3A 0 31.75 31.585 - 31.161 31.082 30.668 3B 30.759 30.927 31.161 31.262 31.75
1 5/16" - 28UN 2A 0.0012 33.307 33.142 - 32.718 32.614 32.225 2B 32.36 32.563 32.748 32.883 33.338
1 5/16" - 28UN 3A 0 33.338 33.172 - 32.748 32.669 32.255 3B 32.36 32.515 32.748 32.85 33.338
1 3/8" - 28UN 2A 0.0012 34.895 34.729 - 34.305 34.201 33.812 2B 33.934 34.163 34.336 34.47 34.925
1 3/8" - 28UN 3A 0 34.925 34.76 - 34.336 34.257 33.843 3B 33.934 34.102 34.336 34.437 34.925
1 7/16" - 28UN 2A 0.0013 36.479 36.314 - 35.89 35.784 35.397 2B 35.535 35.738 35.923 36.063 36.513
1 7/16" - 28UN 3A 0 36.513 36.347 - 35.923 35.844 35.43 3B 35.535 35.69 35.923 36.027 36.513
1 1/2" - 28UN 2A 0.0013 38.067 37.902 - 37.478 37.371 36.985 2B 37.109 37.338 37.511 37.65 38.1
1 1/2" - 28UN 3A 0 38.1 37.935 - 37.511 37.432 37.018 3B 37.109 37.277 37.511 37.615 38.1