Table 3. Standard Series and Selected Combinations—Unified Screw Threads Table 3. (Continued) Standard Series and Selected Combinations—Unified Screw Threads
External b
Internal b
Nominal Size, Threads per Inch, and Series Designation a
Major Diameter
UNR Minor Dia., c Max (Ref.)
Major Diameter
Pitch Diameter
Minor Diameter
Pitch Diameter
Allow ance
Max d
Min e
Max d
Class
Min
Min
Min
Max
Min
Max
Min 3.0000 3.0000 3.0000 3.0000 3.0000 3.0000 3.0000 3.0000 3.0000 3.0000 3.0000 3.0000 3.0000 3.0000 3.0000 3.0000 3.1250 3.1250 3.1250 3.1250 3.1250 3.1250 3.1250 3.1250 3.2500 3.2500 3.2500 3.2500 3.2500
Class
3-4 UNC
1A 0.0032 2.9968 2.9611
— 2.8344 2.8183
2.6991 2.6991 2.7023 2.7987 2.8015 2.8486 2.8512 2.8789 2.8989 2.9008 2.9131 2.9239 2.9256 2.9322 2.9389 2.9405 2.9237 2.9265 2.9736 2.9762 3.0239 3.0258 3.0849 3.0506 2.9490 2.9490 2.9523 3.0487 3.0515
1B 2.729 2B 2.729
2.767 2.767
2.8376 2.8585 2.8376 2.8515 2.8376 2.8480 2.8917 2.9038 2.8917 2.9008 2.9188 2.9299 2.9188 2.9271 2.9350 2.9439 2.9459 2.9541 2.9459 2.9521 2.9536 2.9613 2.9594 2.9667 2.9594 2.9649 2.9639 2.9709 2.9675 2.9743 2.9675 2.9726 3.0167 3.0289 3.0167 3.0259 3.0438 3.0550 3.0438 3.0522 3.0709 3.0792 3.0709 3.0771 3.0844 3.0918 3.0844 3.0899 3.0876 3.1088 3.0876 3.1017 3.0876 3.0982 3.1417 3.1540 3.1417 3.1509
2A 0.0032 2.9968 2.9730 2.9611 2.8344 2.8237
3A 0.0000 3.0000 2.9762 2A 0.0028 2.9972 2.9790 3A 0.0000 3.0000 2.9818 3A 0.0000 3.0000 2.9850 2A 0.0020 2.9980 2.9851 2A 0.0019 2.9981 2.9867 3A 0.0000 3.0000 2.9886 2A 0.0018 2.9982 2.9879 2A 0.0017 2.9983 2.9889 3A 0.0000 3.0000 2.9906 2A 0.0016 2.9984 2.9897 2A 0.0016 2.9984 2.9903 3A 0.0000 3.0000 2.9919 2A 0.0028 3.1222 3.1040 3A 0.0000 3.1250 3.1068 2A 0.0026 3.1224 3.1074 3A 0.0000 3.1250 3.1100 2A 0.0019 3.1231 3.1117 3A 0.0000 3.1250 3.1136 2A 0.0017 3.1233 3.1139 3A 0.0000 3.1250 3.1156 1A 0.0033 3.2467 3.2110 3A 0.0000 3.2500 3.2262 2A 0.0028 3.2472 3.2290 3A 0.0000 3.2500 3.2318
— 2.8376 2.8296 — 2.8889 2.8796 — 2.8917 2.8847 — 2.9188 2.9124 — 2.9330 2.9262 — 2.9440 2.9377 — 2.9459 2.9412 — 2.9518 2.9459 — 2.9577 2.9521 — 2.9594 2.9552 — 2.9623 2.9569 — 2.9659 2.9607 — 2.9675 2.9636 — 3.0139 3.0045 — 3.0167 3.0097 — 3.0412 3.0326 — 3.0438 3.0374 — 3.0690 3.0626 — 3.0709 3.0661 — 3.0827 3.0770 — 3.0844 3.0801 — 3.0843 3.0680 — 3.0876 3.0794 — 3.1389 3.1294 — 3.1417 3.1346
3B 2.7290 2.7594
3-6 UN
2B 2.820
2.850
3B 2.8200 2.8396
3-8 UN
2A 0.0026 2.9974 2.9824 2.9749 2.9162 2.9077
2B 2.865
2.890
3B 2.8650 2.8797
3-10 UNS 3-12 UN 3-14 UNS 3-16 UN 3-18 UNS 3-20 UN
2B 2.892 2B 2.910 2B 2.923 2B 2.932 2B 2.940 2B 2.946
2.913 2.928 2.938 2.946 2.953 2.957
3B 2.9100 2.9198
3B 2.9320 2.9409
3B 2.9460 2.9536
2B 2.945
2.975
3 1 ∕ 8 -6 UN
3B 2.9450 2.9646
2B 2.990
3.015
3 1 ∕ 8 -8 UN
3B 2.9900 3.0047
2B 3.035
3.053
3 1 ∕ 8 -12 UN
3B 3.0350 3.0448
2B 3.057
3.071
3 1 ∕ 8 -16 UN
3B 3.0570 3.0659
1B 2.979 2B 2.979
3.017 3.017
3 1 ∕ 4 -4 UNC
2A 0.0033 3.2467 3.2229 3.2110 3.0843 3.0734
3B 2.9790 3.0094
2B 3.070
3.100
3 1 ∕ 4 -6 UN
3B 3.0700 3.0896
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