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6UN - 60 Degree Unified Threads

The 6 thread series (6-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.

1 7/16" - 1 15/16" 2" - 2 7/8" 3" - 4"

6UN 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 7/16" - 6 UN 2A 0.0024 36.452 35.989 - 33.701 33.498 31.412 2B 31.928 32.715 33.762 34.026 36.513
1 7/16" - 6 UN 3A 0 36.513 36.05 - 33.762 33.609 31.473 3B 31.928 32.438 33.762 33.96 36.513
1 1/2" - 6 UN 1A 0.0024 38.039 37.346 - 35.288 34.981 33 1B 33.528 34.29 35.349 35.751 38.1
1 1/2" - 6 UN 2A 0.0024 38.039 37.577 37.346 35.288 35.082 33 2B 33.528 34.29 35.349 35.616 38.1
1 1/2" - 6 UN 3A 0 38.1 37.638 - 35.349 35.194 33.061 3B 33.528 34.026 35.349 35.55 38.1
1 9/16" - 6 UN 2A 0.0024 39.627 39.164 - 36.876 36.667 34.587 2B 35.103 35.89 36.937 37.206 39.688
1 9/16" - 6 UN 3A 0 39.688 39.225 - 36.937 36.782 34.648 3B 35.103 35.613 36.937 37.14 39.688
1 5/8" - 6 UN 2A 0.0025 41.212 40.749 - 38.461 38.252 36.185 2B 36.703 37.465 38.524 38.796 41.275
1 5/8" - 6 UN 3A 0 41.275 40.813 - 38.524 38.367 36.248 3B 36.703 37.201 38.524 38.727 41.275
1 11/16" - 6 UN 2A 0.0025 42.799 42.337 - 40.048 39.837 37.76 2B 38.278 39.065 40.112 40.386 42.863
1 11/16" - 6 UN 3A 0 42.863 42.4 - 40.112 39.954 37.823 3B 38.278 38.788 40.112 40.317 42.863
1 3/4" - 6 UN 2A 0.0025 44.387 43.924 - 41.636 41.425 39.347 2B 39.878 40.64 41.699 41.974 44.45
1 3/4" - 6 UN 3A 0 44.45 43.988 - 41.699 41.539 39.411 3B 39.878 40.376 41.699 41.905 44.45
1 13/16" - 6 UN 2A 0.0025 45.974 45.512 - 43.223 43.01 40.935 2B 41.453 42.24 43.287 43.564 46.038
1 13/16" - 6 UN 3A 0 46.038 45.575 - 43.287 43.127 40.998 3B 41.453 41.963 43.287 43.495 46.038
1 7/8" - 6 UN 2A 0.0025 47.562 47.099 - 44.811 44.597 42.522 2B 43.053 43.815 44.874 45.154 47.625
1 7/8" - 6 UN 3A 0 47.625 47.163 - 44.874 44.714 42.586 3B 43.053 43.551 44.874 45.082 47.625
1 15/16" - 6 UN 2A 0.0026 49.146 48.684 - 46.396 46.18 44.107 2B 44.628 45.415 46.462 46.744 49.213
1 15/16" - 6 UN 3A 0 49.213 48.75 - 46.462 46.299 44.173 3B 44.628 45.138 46.462 46.673 49.213
2" - 6 UN 2A 0.0026 50.734 50.272 - 47.983 47.765 45.695 2B 46.228 46.99 48.049 48.331 50.8
2" - 6 UN 3A 0 50.8 50.338 - 48.049 47.887 45.761 3B 46.228 46.726 48.049 48.26 50.8
2 1/8" - 6 UN 2A 0.0026 53.909 53.447 - 51.158 50.937 48.87 2B 49.403 50.165 51.224 51.511 53.975
2 1/8" - 6 UN 3A 0 53.975 53.513 - 51.224 51.059 48.936 3B 49.403 49.901 51.224 51.438 53.975
2 1/4" - 6 UN 2A 0.0026 57.084 56.622 - 54.333 54.11 52.045 2B 52.578 53.34 54.399 54.689 57.15
2 1/4" - 6 UN 3A 0 57.15 56.688 - 54.399 54.232 52.111 3B 52.578 53.34 54.399 54.615 57.15
2 3/8" - 6 UN 2A 0.0027 60.256 59.794 - 57.506 57.28 55.217 2B 55.753 56.54 57.574 57.866 60.325
2 3/8" - 6 UN 3A 0 60.325 59.863 - 57.574 57.407 55.286 3B 55.753 56.251 57.574 57.793 60.325
2 1/2" - 6 UN 2A 0.0027 63.431 62.969 - 60.681 60.452 58.392 2B 58.928 59.69 60.749 61.044 63.5
2 1/2" - 6 UN 3A 0 63.5 63.038 - 60.749 60.579 58.461 3B 58.928 59.426 60.749 60.97 63.5
2 5/8" - 6 UN 2A 0.0027 66.606 66.144 - 63.856 63.627 61.567 2B 62.103 62.865 63.924 64.224 66.675
2 5/8" - 6 UN 3A 0 66.675 66.213 - 63.924 63.751 61.636 3B 62.103 62.601 63.924 64.148 66.675
2 3/4" - 6 UN 2A 0.0027 69.781 69.319 - 67.031 66.799 64.742 2B 65.278 66.04 67.099 67.401 69.85
2 3/4" - 6 UN 3A 0 69.85 69.388 - 67.099 66.926 64.811 3B 65.278 65.776 67.099 67.325 69.85
2 7/8" - 6 UN 2A 0.0028 72.954 72.492 - 70.203 69.969 67.915 2B 68.453 69.215 70.274 70.579 73.025
2 7/8" - 6 UN 3A 0 73.025 72.563 - 70.274 70.099 67.986 3B 68.453 68.951 70.274 70.503 73.025
3" - 6 UN 2A 0.0028 76.129 75.667 - 73.378 73.142 71.09 2B 71.628 72.39 73.449 73.757 76.2
3" - 6 UN 3A 0 76.2 75.738 - 73.449 73.271 71.161 3B 71.628 72.126 73.449 73.68 76.2
3 1/8" - 6 UN 2A 0.0028 79.304 78.842 - 76.553 76.314 74.265 2B 74.803 75.565 76.624 76.934 79.375
3 1/8" - 6 UN 3A 0 79.375 78.913 - 76.624 76.446 74.336 3B 74.803 75.301 76.624 76.858 79.375
3 1/4" - 6 UN 2A 0.0028 82.479 82.017 - 79.728 79.487 77.44 2B 77.978 78.74 79.799 80.112 82.55
3 1/4" - 6 UN 3A 0 82.55 82.088 - 79.799 79.619 77.511 3B 77.978 78.476 79.799 80.033 82.55
3 3/8" - 6 UN 2A 0.0029 85.651 85.189 - 82.901 82.659 80.612 2B 81.153 81.915 82.974 83.289 85.725
3 3/8" - 6 UN 3A 0 85.725 85.263 - 82.974 82.791 80.686 3B 81.153 81.651 82.974 83.21 85.725
3 1/2" - 6 UN 2A 0.0029 88.826 88.364 - 86.076 85.832 83.787 2B 84.328 85.09 86.149 86.467 88.9
3 1/2" - 6 UN 3A 0 88.9 88.438 - 86.149 85.966 83.861 3B 84.328 84.826 86.149 86.388 88.9
3 5/8" - 6 UN 2A 0.0029 92.001 91.539 - 89.251 89.004 86.962 2B 87.503 88.265 89.324 89.644 92.075
3 5/8" - 6 UN 3A 0 92.075 91.613 - 89.324 89.139 87.036 3B 87.503 88.001 89.324 89.565 92.075
3 3/4" - 6 UN 2A 0.0029 95.176 94.714 - 92.426 92.177 90.137 2B 90.678 91.44 92.499 92.822 95.25
3 3/4" - 6 UN 3A 0 95.25 94.788 - 92.499 92.314 90.211 3B 90.678 91.176 92.499 92.74 95.25
3 7/8" - 6 UN 2A 0.003 98.349 97.887 - 95.598 95.347 93.309 2B 93.853 94.615 95.674 95.999 98.425
3 7/8" - 6 UN 3A 0 98.425 97.963 - 95.674 95.486 93.386 3B 93.853 94.351 95.674 95.918 98.425
4" - 6 UN 2A 0.003 101.524 101.062 - 98.773 98.522 96.484 2B 97.028 97.79 98.849 99.177 101.6
4" - 6 UN 3A 0 101.6 101.138 - 98.849 98.661 96.561 3B 97.028 97.526 98.849 99.096 101.6