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12UN - 60 Degree Unified Threads

with Controlled Root Radius and Increased Minor Diameter

The 12-thread series (12-UN) is a uniform pitch series for large diameters requiring threads of medium-fine pitch. Although originally intended for boiler practice, it is now used as a continuation of the Fine-Thread Series for diameters larger than 11⁄2 inches.

5/8" - 1 7/16" 1 9/16" - 2 1/8" 2 1/4"- 3 1/8" 3 1/4" - 6"

12UN 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
5/8" - 12 UN 2A 0.0016 15.834 15.545 - 14.46 14.323 13.315 2B 13.589 14.046 14.501 14.681 15.875
5/8" - 12 UN 3A 0 15.875 15.585 - 14.501 14.397 13.355 3B 13.589 13.876 14.501 14.635 15.875
11/16" - 12 UN 2A 0.0016 17.422 17.132 - 16.048 15.911 14.902 2B 15.164 15.621 16.088 16.269 17.463
11/16" - 12 UN 3A 0 17.463 17.173 - 16.088 15.984 14.943 3B 15.164 15.456 16.088 16.223 17.463
3/4" - 12 UN 2A 0.0017 19.007 18.717 - 17.633 17.493 16.487 2B 16.764 17.221 17.676 17.859 19.05
3/4" - 12 UN 3A 0 19.05 18.76 - 17.676 17.572 16.53 3B 16.764 17.036 17.676 17.813 19.05
13/16" - 12 UN 2A 0.0017 20.594 20.305 - 19.22 19.08 18.075 2B 18.339 18.796 19.263 19.446 20.638
13/16" - 12 UN 3A 0 20.638 20.348 - 19.263 19.159 18.118 3B 18.339 18.616 19.263 19.401 20.638
7/8" - 12 UN 2A 0.0017 22.182 21.892 - 20.808 20.668 19.662 2B 19.939 20.396 20.851 21.034 22.225
7/8" - 12 UN 3A 0 22.225 21.935 - 20.851 20.747 19.705 3B 19.939 20.188 20.851 20.988 22.225
15/16" - 12 UN 2A 0.0017 23.769 23.48 - 22.395 22.25 21.25 2B 21.514 21.971 22.438 22.626 23.813
15/16" - 12 UN 3A 0 23.813 23.523 - 22.438 22.334 21.293 3B 21.514 21.781 22.438 22.578 23.813
1 1/16" - 12 UN 2A 0.0017 26.944 26.655 - 25.57 25.425 24.425 2B 24.689 25.146 25.613 25.801 26.988
1 1/16" - 12 UN 3A 0 26.988 26.698 - 25.613 25.507 24.468 3B 24.689 24.95 25.613 25.753 26.988
1 3/8" - 12 UN 2A 0.0017 30.119 29.83 - 28.745 28.598 27.6 2B 27.864 28.321 28.788 28.979 30.163
1 3/8" - 12 UN 3A 0 30.163 29.873 - 28.788 28.679 27.643 3B 27.864 28.125 28.788 28.931 30.163
1 5/16" - 12 UN 2A 0.0017 33.294 33.005 - 31.92 31.773 30.775 2B 31.039 31.496 31.963 32.154 33.338
1 5/16" - 12 UN 3A 0 33.338 33.048 - 31.963 31.854 30.818 3B 31.039 31.3 31.963 32.106 33.338
1 7/16" - 12 UN 2A 0.0018 36.467 36.177 - 35.093 34.943 33.947 2B 34.214 34.671 35.138 35.331 36.513
1 7/16" - 12 UN 3A 0 36.513 36.223 - 35.138 35.027 33.993 3B 34.214 34.475 35.138 35.283 36.513
1 9/16" - 12 UN 2A 0.0018 39.642 39.352 - 38.268 38.118 37.122 2B 37.389 37.846 38.313 38.506 39.688
1 9/16" - 12 UN 3A 0 39.688 39.398 - 38.313 38.202 37.168 3B 37.389 37.65 38.313 38.458 39.688
1 5/8" - 12 UN 2A 0.0018 41.229 40.94 - 39.855 39.705 38.71 2B 38.989 39.446 39.901 40.094 41.275
1 5/8" - 12 UN 3A 0 41.275 40.985 - 39.901 39.789 38.755 3B 38.989 39.238 39.901 40.046 41.275
1 11/16" - 12 UN 2A 0.0018 42.817 42.527 - 41.443 41.29 40.297 2B 40.564 41.021 41.488 41.686 42.863
1 11/16" - 12 UN 3A 0 42.863 42.573 - 41.488 41.374 40.343 3B 40.564 40.825 41.488 41.636 42.863
1 3/4" - 12 UN 2A 0.0018 44.404 44.115 - 43.03 42.878 41.885 2B 42.164 42.621 43.076 43.274 44.45
1 3/4" - 12 UN 3A 0 44.45 44.16 - 43.076 42.962 41.93 3B 42.164 42.413 43.076 43.223 44.45
1 13/16" - 12 UN 2A 0.0018 45.992 45.702 - 44.618 44.465 43.472 2B 43.739 44.196 44.663 44.861 46.038
1 13/16" - 12 UN 3A 0 46.038 45.748 - 44.663 44.549 43.518 3B 43.739 44 44.663 44.811 46.038
1 7/8" - 12 UN 2A 0.0018 47.579 47.29 - 46.205 46.053 45.06 2B 45.339 45.796 46.251 46.449 47.625
1 7/8" - 12 UN 3A 0 47.625 47.335 - 46.251 46.137 45.105 3B 45.339 45.588 46.251 46.398 47.625
1 15/16" - 12 UN 2A 0.0018 49.167 48.877 - 47.793 47.638 46.647 2B 46.914 47.371 47.838 48.039 49.213
1 15/16" - 12 UN 3A 0 49.213 48.923 - 47.838 47.724 46.693 3B 46.914 47.175 47.838 47.988 49.213
2" - 12 UN 2A 0.0018 50.754 50.465 - 49.38 49.225 48.235 2B 48.514 48.971 49.426 49.627 50.8
2" - 12 UN 3A 0 50.8 50.51 - 49.426 49.312 48.28 3B 48.514 48.763 49.426 49.576 50.8
2 1/8" - 12 UN 2A 0.0018 53.929 53.64 - 52.555 52.4 51.41 2B 51.689 52.146 52.601 52.802 53.975
2 1/8" - 12 UN 3A 0 53.975 53.685 - 52.601 52.487 51.455 3B 51.689 51.938 52.601 52.751 53.975
2 1/4" - 12 UN 2A 0.0018 57.104 56.815 - 55.73 55.575 54.585 2B 54.864 55.321 55.776 55.977 57.15
2 1/4" - 12 UN 3A 0 57.15 56.86 - 55.776 55.662 54.63 3B 54.864 55.321 55.776 55.926 57.15
2 3/8" - 12 UN 2A 0.0019 60.277 59.987 - 58.903 58.745 57.757 2B 58.039 58.496 58.951 59.157 60.325
2 3/8" - 12 UN 3A 0 60.325 60.035 - 58.951 58.834 57.805 3B 58.039 58.288 58.951 59.103 60.325
2 1/2" - 12 UN 2A 0.0019 63.452 63.162 - 62.078 61.92 60.932 2B 61.214 61.671 62.126 62.332 63.5
2 1/2" - 12 UN 3A 0 63.5 63.21 - 62.126 62.009 60.98 3B 61.214 61.463 62.126 62.278 63.5
2 5/8" - 12 UN 2A 0.0019 66.627 66.337 - 65.253 65.095 64.107 2B 64.389 64.846 65.301 65.507 66.675
2 5/8" - 12 UN 3A 0 66.675 66.385 - 65.301 65.184 64.155 3B 64.389 64.638 65.301 65.453 66.675
2 3/4" - 12 UN 2A 0.0019 69.802 69.512 - 68.428 68.27 67.282 2B 67.564 68.021 68.476 68.682 69.85
2 3/4" - 12 UN 3A 0 69.85 69.56 - 68.476 68.359 67.33 3B 67.564 67.813 68.476 68.628 69.85
2 7/8" - 12 UN 2A 0.0019 72.977 72.687 - 71.603 71.443 70.457 2B 70.739 71.196 71.651 71.859 73.025
2 7/8" - 12 UN 3A 0 73.025 72.735 - 71.651 71.531 70.505 3B 70.739 70.988 71.651 71.808 73.025
3" - 12 UN 2A 0.0019 76.152 75.862 - 74.778 74.618 73.632 2B 73.914 74.371 74.826 75.034 76.2
3" - 12 UN 3A 0 76.2 75.91 - 74.826 74.706 73.68 3B 73.914 74.163 74.826 74.983 76.2
3 1/8" - 12 UN 2A 0.0019 79.327 79.037 - 77.953 77.793 76.807 2B 77.089 77.546 78.001 78.209 79.375
3 1/8" - 12 UN 3A 0 79.375 79.085 - 78.001 77.881 76.855 3B 77.089 77.338 78.001 78.158 79.375
3 1/4" - 12 UN 2A 0.0019 82.502 82.212 - 81.128 80.968 79.982 2B 80.264 80.721 81.176 81.384 82.55
3 1/4" - 12 UN 3A 0 82.55 82.26 - 81.176 81.056 80.03 3B 80.264 80.513 81.176 81.384 82.55
3 3/8" - 12 UN 2A 0.0019 85.677 85.387 - 84.303 84.14 83.157 2B 83.439 83.896 84.351 84.564 85.725
3 3/8" - 12 UN 3A 0 85.725 85.435 - 84.351 84.229 83.205 3B 83.439 83.688 84.351 84.511 85.725
3 1/2" - 12 UN 2A 0.0019 88.852 88.562 - 87.478 87.315 86.332 2B 86.614 87.071 87.526 87.739 88.9
3 1/2" - 12 UN 3A 0 88.9 88.61 - 87.526 87.404 86.38 3B 86.614 86.863 87.526 87.686 88.9
3 5/8" - 12 UN 2A 0.0019 92.027 91.737 - 90.653 90.49 89.507 2B 89.789 90.246 90.701 90.914 92.075
3 5/8" - 12 UN 3A 0 92.075 91.785 - 90.701 90.579 89.555 3B 89.789 90.038 90.701 90.861 92.075
3 3/4" - 12 UN 2A 0.0019 95.202 94.912 - 93.828 93.665 92.682 2B 92.964 93.421 93.876 94.089 95.25
3 3/4" - 12 UN 3A 0 95.25 94.96 - 93.876 93.754 92.73 3B 92.964 93.213 93.876 94.036 95.25
3 7/8" - 12 UN 2A 0.002 98.374 98.085 - 97 96.835 95.855 2B 96.139 96.596 97.051 97.267 98.425
3 7/8" - 12 UN 3A 0 98.425 98.135 - 97.051 96.926 95.905 3B 96.139 96.388 97.051 97.213 98.425
4" - 12 UN 2A 0.002 101.549 101.26 - 100.175 100.01 99.03 2B 99.314 99.771 100.226 100.442 101.6
4" - 12 UN 3A 0 101.6 101.31 - 100.226 100.101 99.08 3B 99.314 99.563 100.226 100.388 101.6
4 1/4" - 12 UN 2A 0.002 107.899 107.61 - 106.525 106.36 105.38 2B 105.664 106.121 106.576 106.792 107.95
4 1/4" - 12 UN 3A 0 107.95 107.66 - 106.576 106.451 105.43 3B 105.664 105.913 106.576 106.738 107.95
5 3/4" - 12 UN 2A 0.0021 145.997 145.707 - 144.623 144.447 143.477 2B 143.764 144.221 144.676 144.904 146.05
5 3/4" - 12 UN 3A 0 146.05 145.76 - 144.676 144.544 143.53 3B 143.764 144.013 144.676 144.846 146.05
6" - 12 UN 2A 0.0021 152.347 152.057 - 150.973 150.797 149.827 2B 150.114 150.571 151.026 151.254 152.4
6" - 12 UN 3A 0 152.4 152.11 - 151.026 150.894 149.88 3B 150.114 150.363 151.026 151.196 152.4