engineering fundamentals Unified Screw Threads, Standard Series
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Nominal Thread SizeCovered Range
0-80 UNF to ¼-56 UNS Nominal thread sizes from 0-80 UNF to ¼-56 UNS
5/16-18 UNC to 9/16 -32 UN Nominal thread sizes from 5/16-18 UNC to 9/16 -32 UN
5/8-11 UNC to 7/8-32 UN Nominal thread sizes from 5/8-11 UNC to 7/8-32 UN
15/16-12 UN to 1 3/16-28 UN Nominal thread sizes from 15/16-12 UN to 1 3/16-28 UN
1 1/4-7 UNC to 1 9/16-20 UN Nominal thread sizes from 1 1/4-7 UNC to 1 9/16-20 UN
1 5/8-6 UN to 1 15/16-20 UN Nominal thread sizes from 1 5/8-6 UN to 1 15/16-20 UN
2-4½ UNC to 2¾-20 UN Nominal thread sizes from 2-4½ UNC to 2¾-20 UN
2 7/8-6 UN to 4-16 UN Nominal thread sizes from 2 7/8-6 UN to 4-16 UN
 
External Thread /Internal Thread
  Nominal Size, TPI, Series Class Allowance Maxa Major
Max Minor
Min Major
Min Minor
Min b Maxa Pitch Min Pitch UNRc Minor Dia
Major Dia(Min)
Ext. 15/16-12 UN 2A 0.0017 0.9358 0.9244 - 0.8817 0.8760 0.8366
Int.   2B   0.8650 0.8470   0.8908 0.8834 0.9375
Ext. 15/16-12 UN 3A 0.0000 0.9375 0.9261 - 0.8834 0.8793 0.8383
Int.   3B   0.8575 0.8470   0.8889 0.8834 0.9375
Ext. 15/16-16 UN 2A 0.0015 0.9360 0.9266 - 0.8954 0.8904 0.8615
Int.   2B   0.8840 0.8700   0.9034 0.8969 0.9375
Ext. 15/16-16 UN 3A 0.0000 0.9375 0.9281 - 0.8969 0.8932 0.8630
Int.   3B   0.8783 0.8700   0.9018 0.8969 0.9375
Ext. 15/16-20 UNEF 2A 0.0014 0.9361 0.9280 - 0.9036 0.8991 0.8766
Int.   2B   0.8950 0.8830   0.9109 0.9050 0.9375
Ext. 15/16-20 UNEF 3A 0.0000 0.9375 0.9294 - 0.9050 0.9016 0.8780
Int.   3B   0.8912 0.8830   0.9094 0.9050 0.9375
Ext. 15/16-28 UN 2A 0.0012 0.9363 0.9298 - 0.9131 0.9091 0.8937
Int.   2B   0.9070 0.8990   0.9195 0.9143 0.9375
Ext. 15/16-28 UN 3A 0.0000 0.9375 0.9310 - 0.9143 0.9113 0.8949
Int.   3B   0.9051 0.8990   0.9182 0.9143 0.9375
Ext. 15/16-32 UN 2A 0.0011 0.9364 0.9304 - 0.9161 0.9123 0.8992
Int.   2B   0.9110 0.9040   0.9221 0.9172 0.9375
Ext. 15/16-32 UN 3A 0.0000 0.9375 0.9315 - 0.9172 0.9144 0.9003
Int.   3B   0.9094 0.9040   0.9209 0.9172 0.9375
Ext. 1-8 UNC 1A 0.0020 0.9980 0.9755 - 0.9168 0.9067 0.8492
Int.   1B   0.8900 0.8650   0.9320 0.9188 1.0000
Ext. 1-8 UNC 2A 0.0020 0.9980 0.9830 0.9755 0.9168 0.9100 0.8492
Int.   2B   0.8900 0.8650   0.9276 0.9188 1.0000
Ext. 1-8 UNC 3A 0.0000 1.0000 0.9850 - 0.9188 0.9137 0.8512
Int.   3B   0.8797 0.8650   0.9254 0.9188 1.0000
Ext. 1-10 UNS 2A 0.0018 0.9982 0.9853 - 0.9332 0.9270 0.8792
Int.   2B   0.9130 0.8920   0.9430 0.9350 1.0000
Ext. 1-12 UNF 1A 0.0018 0.9982 0.9810 - 0.9441 0.9353 0.8990
Int.   1B   0.9280 0.9100   0.9573 0.9459 1.0000
Ext. 1-12 UNF 2A 0.0018 0.9982 0.9868 - 0.9441 0.9382 0.8990
Int.   2B   0.9280 0.9100   0.9535 0.9459 1.0000
Ext. 1-12 UNF 3A 0.0000 1.0000 0.9886 - 0.9459 0.9415 0.9008
Int.   3B   0.9198 0.9100   0.9516 0.9459 1.0000
Ext. 1-14UNS 1A 0.0017 0.9983 0.9828 - 0.9519 0.9435 0.9132
Int.   1B   0.9380 0.9230   0.9645 0.9536 1.0000
Ext. 1-14UNS 2A 0.0017 0.9983 0.9880 - 0.9519 0.9463 0.9132
Int.   2B   0.9380 0.9230   0.9609 0.9536 1.0000
Ext. 1-14UNS 3A 0.0000 1.0000 0.9897 - 0.9536 0.9494 0.9149
Int.   3B   0.9315 0.9230   0.9590 0.9536 1.0000
Ext. 1-16 UN 2A 0.0015 0.9985 0.9891 - 0.9579 0.9529 0.9240
Int.   2B   0.9460 0.9320   0.9659 0.9594 1.0000
Ext. 1-16 UN 3A 0.0000 1.0000 0.9906 - 0.9594 0.9557 0.9255
Int.   3B   0.9408 0.9320   0.9643 0.9594 1.0000
Ext. 1-18 UNS 2A 0.0014 0.9986 0.9899 - 0.9625 0.9578 0.9325
Int.   2B   0.9530 0.9400   0.9701 0.9639 1.0000
Ext. 1-20 UNEF 2A 0.0014 0.9986 0.9905 - 0.9661 0.9616 0.9391
Int.   2B   0.9570 0.9460   0.9734 0.9675 1.0000
Ext. 1-20 UNEF 3A 0.0000 1.0000 0.9919 - 0.9675 0.9641 0.9405
Int.   3B   0.9537 0.9460   0.9719 0.9675 1.0000
Ext. 1-24 UNS 2A 0.0013 0.9987 0.9915 - 0.9716 0.9674 0.9491
Int.   2B   0.9650 0.9550   0.9784 0.9729 1.0000
Ext. 1-27 UNS 2A 0.0012 0.9988 0.9921 - 0.9747 0.9707 0.9547
Int.   2B   0.9690 0.9600   0.9811 0.9759 1.0000
Ext. 1-28 UN 2A 0.0012 0.9988 0.9923 - 0.9756 0.9716 0.9562
Int.   2B   0.9700 0.9610   0.9820 0.9768 1.0000
Ext. 1-28 UN 3A 0.0000 1.0000 0.9935 - 0.9768 0.9738 0.9574
Int.   3B   0.9676 0.9610   0.9807 0.9768 1.0000
Ext. 1-32 UN 2A 0.0011 0.9989 0.9929 - 0.9786 0.9748 0.9617
Int.   2B   0.9740 0.9660   0.9846 0.9797 1.0000
Ext. 1-32 UN 3A 0.0000 1.0000 0.9940 - 0.9797 0.9769 0.9628
Int.   3B   0.9719 0.9660   0.9834 0.9797 1.0000
Ext. 11/16-8 UN 2A 0.0020 1.0605 1.0455 - 0.9793 0.9725 0.9117
Int.   2B   0.9520 0.9270   0.9902 0.9813 1.0625
Ext. 11/16-8 UN 3A 0.0000 1.0625 1.0475 - 0.9813 0.9762 0.9137
Int.   3B   0.9422 0.9270   0.9880 0.9813 1.0625
Ext. 11/16-12 UN 2A 0.0017 1.0608 1.0494 - 1.0067 1.0010 0.9616
Int.   2B   0.9900 0.9720   1.0158 1.0084 1.0625
Ext. 11/16-12 UN 3A 0.0000 1.0625 1.0511 - 1.0084 1.0042 0.9633
Int.   3B   0.9823 0.9720   1.0139 1.0084 1.0625
Ext. 11/16-16 UN 2A 0.0015 1.0610 1.0516 - 1.0204 1.0154 0.9865
Int.   2B   1.0090 0.9950   1.0284 1.0219 1.0625
Ext. 11/16-16 UN 3A 0.0000 1.0625 1.0531 - 1.0219 1.0182 0.9880
Int.   3B   1.0033 0.9950   1.0268 1.0219 1.0625
Ext. 11/16-18 UNEF 2A 0.0014 1.0611 1.0524 - 1.0250 1.0203 0.9950
Int.   2B   1.0150 1.0020   1.0326 1.0264 1.0625
Ext. 11/16-18 UNEF 3A 0.0000 1.0625 1.0538 - 1.0264 1.0228 0.9964
Int.   3B   1.0105 1.0020   1.0310 1.0264 1.0625
Ext. 11/16-20 UN 2A 0.0014 1.0611 1.0530 - 1.0286 1.0241 1.0016
Int.   2B   1.0200 1.0080   1.0359 1.0300 1.0625
Ext. 11/16-20 UN 3A 0.0000 1.0625 1.0544 - 1.0300 1.0266 1.0030
Int.   3B   1.0162 1.0080   1.0344 1.0300 1.0625
Ext. 11/16-28 UN 2A 0.0012 1.0613 1.0548 - 1.0381 1.0341 1.0187
Int.   2B   1.0320 1.0240   1.0445 1.0393 1.0625
Ext. 11/16-28 UN 3A 0.0000 1.0625 1.0560 - 1.0393 1.0363 1.0199
Int.   3B   1.0301 1.0240   1.0432 1.0393 1.0625
Ext. 11/8-7 UNC 1A 0.0022 1.1228 1.0982 - 1.0300 1.0191 0.9527
Int.   1B   0.9980 0.9700   1.0463 1.0322 1.1250
Ext. 11/8-7 UNC 2A 0.0022 1.1228 1.1064 1.0982 1.0300 1.0228 0.9527
Int.   2B   0.9980 0.9700   1.0416 1.0322 1.1250
Ext. 11/8-7 UNC 3A 0.0000 1.1250 1.1086 - 1.0322 1.0268 0.9549
Int.   3B   0.9875 0.9700   1.0393 1.0322 1.1250
Ext. 11/8-8 UN 2A 0.0021 1.1229 1.1079 1.1004 1.0417 1.0348 0.9741
Int.   2B   1.0150 0.9900   1.0528 1.0438 1.1250
Ext. 11/8-8 UN 3A 0.0000 1.1250 1.1100 - 1.0438 1.0386 0.9762
Int.   3B   1.0047 0.9900   1.0505 1.0438 1.1250
Ext. 11/8-10 UNS 2A 0.0018 1.1232 1.1103 - 1.0582 1.0520 1.0042
Int.   2B   1.0380 1.0170   1.0680 1.0600 1.1250
Ext. 11/8-12 UNF 1A 0.0018 1.1232 1.1060 - 1.0691 1.0601 1.0240
Int.   1B   1.0530 1.0350   1.0826 1.0709 1.1250
Ext. 11/8-12 UNF 2A 0.0018 1.1232 1.1118 - 1.0691 1.0631 1.0240
Int.   2B   1.0530 1.0350   1.0787 1.0709 1.1250
Ext. 11/8-12 UNF 3A 0.0000 1.1250 1.1136 - 1.0709 1.0664 1.0258
Int.   3B   1.0448 1.0350   1.0768 1.0709 1.1250
Ext. 11/8-14 UNS 2A 0.0016 1.1234 1.1131 - 1.0770 1.0717 1.0384
Int.   2B   1.0640 1.0480   1.0855 1.0786 1.1250
Ext. 11/8-16 UN 2A 0.0015 1.1235 1.1141 - 1.0829 1.0779 1.0490
Int.   2B   1.0710 1.0570   1.0909 1.0844 1.1250
Ext. 11/8-16 UN 3A 0.0000 1.1250 1.1156 - 1.0844 1.0807 1.0505
Int.   2B   1.0658 1.0570   1.0893 1.0844 1.1250
Ext. 11/8-18 UNEF 2A 0.0014 1.1236 1.1149 - 1.0875 1.0828 1.0575
Int.   2B   1.0780 1.0650   1.0951 1.0889 1.1250
Ext. 11/8-18 UNEF 3A 0.0000 1.1250 1.1163 - 1.0889 1.0853 1.0589
Int.   3B   1.0730 1.0650   1.0935 1.0889 1.1250
Ext. 11/8-20 UN 2A 0.0014 1.1236 1.1155 - 1.0911 1.0866 1.0641
Int.   2B   1.0820 1.0710   1.0984 1.0925 1.1250
Ext. 11/8-20 UN 3A 0.0000 1.1250 1.1169 - 1.0925 1.0891 1.0655
Int.   3B   1.0787 1.0710   1.0969 1.0925 1.1250
Ext. 11/8-24 UNS 2A 0.0013 1.1237 1.1165 - 1.0966 1.0924 1.0742
Int.   2B   1.0900 1.0800   1.1034 1.0979 1.1250
Ext. 11/8-28 UN 2A 0.0012 1.1238 1.1173 - 1.1006 1.0966 1.0812
Int.   2B   1.0950 1.0860   1.1070 1.1018 1.1250
Ext. 11/8-28 UN 3A 0.0000 1.1250 1.1185 - 1.1018 1.0988 1.0824
Int.   3B   1.0926 1.0860   1.1057 1.1018 1.1250
Ext. 13/16-8 UN 2A 0.0021 1.1854 1.1704 - 1.1042 1.0972 1.0366
Int.   2B   1.0770 1.0520   1.1154 1.1063 1.1875
Ext. 13/16-8 UN 3A 0.0000 1.1875 1.1725 - 1.1063 1.1011 1.0387
Int.   3B   1.0672 1.0520   1.1131 1.1063 1.1875
Ext. 13/16-12 UN 2A 1.0017 1.1858 1.1744 - 1.1317 1.1259 1.0866
Int.   2B   1.1150 1.0970   1.1409 1.1334 1.1875
Ext. 13/16-12 UN 3A 0.0000 1.1872 1.1761 - 1.1334 1.1291 1.0883
Int.   3B   1.1073 1.0970   1.1390 1.1334 1.1875
Ext. 13/16-16 UN 2A 0.0015 1.1860 1.1766 - 1.1454 1.1403 1.1115
Int.   2B   1.1340 1.1200   1.1535 1.1469 1.1875
Ext. 13/16-16 UN 3A 0.0000 1.1875 1.1781 - 1.1469 1.1431 1.1130
Int.   3B   1.1283 1.1200   1.1519 1.1469 1.1875
Ext. 13/16-18 UNEF 2A 0.0015 1.1860 1.1773 - 1.1499 1.1450 1.1199
Int.   2B   1.1400 1.1270   1.1577 1.1514 1.1875
Ext. 13/16-18 UNEF 3A 0.0000 1.1875 1.1788 - 1.1514 1.1478 1.1214
Int.   3B   1.1355 1.1270   1.1561 1.1514 1.1875
Ext. 13/16-20 UN 2A 0.0014 1.1861 1.1780 - 1.1536 1.1489 1.1266
Int.   2B   1.1450 1.1330   1.1611 1.1550 1.1875
Ext. 13/16-20 UN 3A 0.0000 1.1875 1.1794 - 1.1550 1.1515 1.1280
Int.   3B   1.1412 1.1330   1.1595 1.1550 1.1875
Ext. 13/16-28 UN 2A 0.0012 1.1863 1.1798 - 1.1631 1.1590 1.1437
Int.   2B   1.1570 1.1490   1.1696 1.1643 1.1875
Ext. 13/16-28 UN 3A 0.0000 1.1875 1.1810 - 1.1643 1.1612 1.1449
Int.   3B   1.1551 1.1490   1.1683 1.1643 1.1875
a For Class 2A threads with coating (plating) the max. is increased by the allowance, to the basic size. This is the same value as Class 3A.
b For uncoated hot-rolled, but not standard fasteners with cold rolled threads
c UN series external thread, Max.Diameter = Basic - Allowance, for Class 1A and 2A
  = Basic for Class 3A
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