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8UN - 60 Degree Unified Threads

The 8-thread series (8-UN) is a uniform-pitch series for large diame- ters. Although originally intended for high-pressure-joint bolts and nuts, it is now widely used as a substitute for the Coarse-Thread Series for diameters larger than 1 inch.

1 1/16" - 1 11/16" 1 3/4" - 2 5/8" 2 3/4" - 3 3/4" 3 7/8" - 4"

8UN 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
1 1/16" - 8 UN 2A 0.002 26.937 26.556 - 24.874 24.702 23.157 2B 23.546 24.181 24.925 25.151 26.988
1 1/16" - 8 UN 3A 0 26.988 26.607 - 24.925 24.795 23.208 3B 23.546 23.932 24.925 25.095 26.988
1 1/8" - 8 UN 2A 0.0021 28.522 28.141 27.95 26.459 26.284 24.742 2B 25.146 25.781 26.513 26.741 28.575
1 1/8" - 8 UN 3A 0 28.575 28.194 - 26.513 26.38 24.795 3B 25.146 25.519 26.513 26.683 28.575
1 3/8" - 8UN 3A 0 34.925 34.463 - 32.174 32.022 29.886 3B 30.353 30.851 32.174 32.372 34.925
1 3/8" - 8UN 2A 0.0022 34.869 34.488 34.298 32.807 32.624 31.09 2B 31.496 32.131 32.863 33.099 34.925
1 1/4" - 8 UN 2A 0.0021 31.697 31.316 31.125 29.634 29.456 27.917 2B 28.321 28.956 29.688 29.921 31.75
1 1/4" - 8 UN 3A 0 31.75 31.369 - 29.688 29.553 27.97 3B 28.321 28.694 29.688 29.863 31.75
1 5/16" - 8 UN 2A 0.0021 33.284 32.903 - 31.222 31.041 29.505 2B 29.896 30.531 31.275 31.509 33.338
1 5/16" - 8 UN 3A 0 33.338 32.957 - 31.275 31.14 29.558 3B 29.896 30.282 31.275 31.45 33.338
1 7/16" - 8 UN 2A 0.0022 36.457 36.076 - 34.394 34.211 32.677 2B 33.071 33.706 34.45 34.689 36.513
1 7/16" - 8 UN 3A 0 36.513 36.132 - 34.45 34.313 32.733 3B 33.071 33.457 34.45 34.63 36.513
1 1/2" - 8 UN 2A 0.0022 38.044 37.663 37.473 35.982 35.796 34.265 2B 34.671 35.306 36.038 36.279 38.1
1 1/2" - 8 UN 3A 0 38.1 37.719 - 36.038 35.898 34.32 3B 34.671 35.044 36.038 36.218 38.1
1 9/16" - 8 UN 2A 0.0022 39.632 39.251 - 37.569 37.381 35.852 2B 36.246 36.881 37.625 37.869 39.688
1 9/16" - 8 UN 3A 0 39.688 39.307 - 37.625 37.485 35.908 3B 36.246 36.632 37.625 37.808 39.688
1 5/8" - 8 UN 2A 0.0022 41.219 40.838 40.648 39.157 38.969 37.551 2B 37.846 38.481 39.213 39.459 41.275
1 5/8" - 8 UN 3A 0 41.275 40.894 - 39.213 39.07 37.607 3B 37.846 38.219 39.213 39.395 41.275
1 11/16" - 8 UN 2A 0.0022 42.807 42.426 - 40.744 40.554 39.027 2B 39.421 40.056 40.8 41.046 42.863
1 11/16" - 8 UN 3A 0 42.863 42.482 - 40.8 40.658 39.083 3B 39.421 39.807 40.8 40.985 42.863
1 3/4" - 8 UN 2A 0.0023 44.392 44.011 43.82 42.329 42.139 40.612 2B 41.021 41.656 42.388 42.636 44.45
1 3/4" - 8 UN 3A 0 44.45 44.069 - 42.388 42.245 40.67 3B 41.021 41.394 42.388 42.575 44.45
1 13/16" - 8 UN 2A 0.0023 45.979 45.598 - 43.917 43.724 42.2 2B 42.596 43.231 43.975 44.226 46.038
1 13/16" - 8 UN 3A 0 46.038 45.657 - 43.975 43.83 42.258 3B 42.596 42.982 43.975 44.163 46.038
1 7/8" - 8 UN 2A 0.0023 47.567 47.186 46.995 45.504 45.309 43.787 2B 44.196 44.831 45.563 45.817 47.625
1 7/8" - 8 UN 3A 0 47.625 47.244 - 45.563 45.418 43.845 3B 44.196 44.569 45.563 45.753 47.625
1 15/16" - 8 UN 2A 0.0023 49.154 48.773 - 47.092 46.896 45.375 2B 45.771 46.406 47.15 47.404 49.213
1 15/16" - 8 UN 3A 0 49.213 48.832 - 47.15 47.003 45.433 3B 45.771 46.157 47.15 47.341 49.213
2" - 8 UN 2A 0.0023 50.742 50.361 50.17 48.679 48.481 46.962 2B 47.371 48.006 48.738 48.994 50.8
2" - 8 UN 3A 0 50.8 50.419 - 48.738 48.59 47.02 3B 47.371 47.744 48.738 48.931 50.8
2 1/8" - 8 UN 2A 0.0024 53.914 53.533 53.343 51.852 51.651 50.135 2B 50.546 51.181 51.913 52.172 53.975
2 1/8" - 8 UN 3A 0 53.975 53.594 - 51.913 51.763 50.195 3B 50.546 50.919 51.913 52.108 53.975
2 1/4" - 8 UN 2A 0.0024 57.089 56.708 56.518 55.027 54.823 53.31 2B 53.721 54.356 55.088 55.352 57.15
2 1/4" - 8 UN 3A 0 57.15 56.769 - 55.088 54.935 53.37 3B 53.721 54.356 55.088 55.286 57.15
2 3/8" - 8 UN 2A 0.0024 60.264 59.883 - 58.202 57.996 56.485 2B 56.896 57.531 58.263 58.529 60.325
2 3/8" - 8 UN 3A 0 60.325 59.944 - 58.263 58.11 56.545 3B 56.896 57.269 58.263 58.463 60.325
2 1/2" - 8 UN 2A 0.0024 63.439 63.058 62.868 61.377 61.168 59.66 2B 60.071 60.706 61.438 61.707 63.5
2 1/2" - 8 UN 3A 0 63.5 63.119 - 61.438 61.283 59.72 3B 60.071 60.444 61.438 61.641 63.5
2 5/8" - 8 UN 2A 0.0025 66.612 66.231 - 64.549 64.341 62.832 2B 63.246 63.881 64.613 64.884 66.675
2 5/8" - 8 UN 3A 0 66.675 66.294 - 64.613 64.455 62.895 3B 63.246 63.619 64.613 64.816 66.675
2 3/4" - 8 UN 2A 0.0025 69.787 69.406 69.215 67.724 67.513 66.007 2B 66.421 67.056 67.788 68.062 69.85
2 3/4" - 8 UN 3A 0 69.85 69.469 - 67.788 67.628 66.07 3B 66.421 66.794 67.788 67.993 69.85
2 7/8" - 8 UN 2A 0.0025 72.962 72.581 - 70.899 70.686 69.182 2B 69.596 70.231 70.963 71.242 73.025
2 7/8" - 8 UN 3A 0 73.025 72.644 - 70.963 70.803 69.245 3B 69.596 69.969 70.963 71.171 73.025
3" - 8 UN 2A 0.0026 76.134 75.753 75.562 74.071 73.856 72.354 2B 72.771 73.406 74.138 74.419 76.2
3" - 8 UN 3A 0 76.2 75.819 - 74.138 73.975 72.42 3B 72.771 73.144 74.138 74.348 76.2
3 1/8" - 8 UN 2A 0.0026 79.309 78.928 - 77.246 77.028 75.529 2B 75.946 76.581 77.313 77.597 79.375
3 1/8" - 8 UN 3A 0 79.375 78.994 - 77.313 77.15 75.595 3B 75.946 76.319 77.313 77.526 79.375
3 1/4" - 8 UN 2A 0.0026 82.484 82.103 81.912 80.421 80.201 78.704 2B 79.121 79.756 80.488 80.775 82.55
3 1/4" - 8 UN 3A 0 82.55 82.169 - 80.488 80.322 78.77 3B 79.121 79.494 80.488 80.703 82.55
3 3/8" - 8 UN 2A 0.0026 85.659 85.278 - 83.596 83.373 81.879 2B 82.296 82.931 83.663 83.952 85.725
3 3/8" - 8 UN 3A 0 85.725 85.344 - 83.663 83.495 81.945 3B 82.296 82.669 83.663 83.878 85.725
3 1/2" - 8 UN 2A 0.0026 88.834 88.453 88.262 86.771 86.548 85.054 2B 85.471 86.106 86.838 87.13 88.9
3 1/2" - 8 UN 3A 0 88.9 88.519 - 86.838 86.67 85.12 3B 85.471 85.844 86.838 87.056 88.9
3 5/8" - 8 UN 2A 0.0027 92.006 91.625 - 89.944 89.718 88.227 2B 88.646 89.281 90.013 90.307 92.075
3 5/8" - 8 UN 3A 0 92.075 91.694 - 90.013 89.842 88.295 3B 88.646 89.019 90.013 90.234 92.075
3 3/4" - 8 UN 2A 0.0027 95.181 94.8 94.61 93.119 92.89 91.402 2B 91.821 92.456 93.188 93.485 95.25
3 3/4" - 8 UN 3A 0 95.25 94.869 - 93.188 93.017 91.47 3B 91.821 92.194 93.188 93.411 95.25
3 7/8" - 8 UN 2A 0.0027 98.356 97.975 - 96.294 96.063 94.577 2B 94.996 95.631 96.363 96.662 98.425
3 7/8" - 8 UN 3A 0 98.425 98.044 - 96.363 96.19 94.645 3B 94.996 95.369 96.363 96.586 98.425
4" - 8 UN 2A 0.0027 101.531 101.15 100.96 99.469 99.238 97.752 2B 98.171 98.806 99.538 99.84 101.6
4" - 8 UN 3A 0 101.6 101.219 - 99.538 99.365 97.82 3B 98.171 98.544 99.538 99.764 101.6