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. 11/4-7 UNC 1A 0.0022 1.2478 1.2232 - 1.1550 1.1439 1.0777
Int.   1B   1.1230 1.0950   1.1716 1.1572 1.2500
Ext. 11/4-7 UNC 2A 0.0022 1.2478 1.2314 1.2232 1.1550 1.1476 1.0777
Int.   2B   1.1230 1.0950   1.1668 1.1572 1.2500
Ext. 11/4-7 UNC 3A 0.0000 1.2500 1.2336 - 1.1572 1.1517 1.0799
Int.   3B   1.1125 1.0950   1.1644 1.1572 1.2500
Ext. 11/4-8 UN 2A 0.0021 1.2479 1.2329 1.2254 1.1667 1.1597 1.0991
Int.   2B   1.1400 1.1150   1.1780 1.1688 1.2500
Ext. 11/4-8 UN 3A 0.0000 1.2500 1.2350 - 1.1688 1.1635 1.1012
Int.   3B   1.1297 1.1150   1.1757 1.1688 1.2500
Ext. 11/4-10 UNS 2A 0.0019 1.2481 1.2352 - 1.1831 1.1768 1.1291
Int.   2B   1.1630 1.1420   1.1932 1.1850 1.2500
Ext. 11/4-12 UNF 1A 0.0018 1.2482 1.2310 - 1.1941 1.1849 1.1490
Int.   1B   1.1780 1.1600   1.2079 1.1959 1.2500
Ext. 11/4-12 UNF 2A 0.0018 1.2482 1.2368 - 1.1941 1.1879 1.1490
Int.   2B   1.1780 1.1600   1.2039 1.1959 1.2500
Ext. 11/4-12 UNF 3A 0.0000 1.2500 1.2386 - 1.1959 1.1913 1.1508
Int.   3B   1.1698 1.1600   1.2019 1.1959 1.2500
Ext. 11/4-14 UNS 2A 0.0016 1.2484 1.2381 - 1.2020 1.1966 1.1634
Int.   2B   1.1880 1.1730   1.2106 1.2036 1.2500
Ext. 11/4-16 UN 2A 0.0015 1.2485 1.2391 - 1.2079 1.2028 1.1740
Int.   2B   1.1960 1.1820   1.2160 1.2094 1.2500
Ext. 11/4-16 UN 3A 0.0000 1.2500 1.2406 - 1.2094 1.2056 1.1755
Int.   3B   1.1908 1.1820   1.2144 1.2094 1.2500
Ext. 11/4-18 UNEF 2A 0.0015 1.2485 1.2398 - 1.2124 1.2075 1.1824
Int.   2B   1.2030 1.1900   1.2202 1.2139 1.2500
Ext. 11/4-18 UNEF 3A 0.0000 1.2500 1.2413 - 1.2139 1.2103 1.1839
Int.   3B   1.1980 1.1900   1.2186 1.2139 1.2500
Ext. 11/4-20 UN 2A 0.0014 1.2486 1.2405 - 1.2161 1.2114 1.1891
Int.   2B   1.2070 1.1960   1.2236 1.2175 1.2500
Ext. 11/4-20 UN 3A 0.0000 1.2500 1.2419 - 1.2175 1.2140 1.1905
Int.   3B   1.2037 1.1960   1.2220 1.2175 1.2500
Ext. 11/4-24 UNS 2A 0.0013 1.2487 1.2415 - 1.2216 1.2173 1.1991
Int.   2B   1.2150 1.2050   1.2285 1.2229 1.2500
Ext. 11/4-28 UN 2A 0.0012 1.2488 1.2423 - 1.2256 1.2215 1.2062
Int.   2B   1.2200 1.2110   1.2321 1.2268 1.2500
Ext. 11/4-28 UN 3A 0.0000 1.2500 1.2435 - 1.2268 1.2237 1.2074
Int.   3B   1.2176 1.2110   1.2308 1.2268 1.2500
Ext. 15/16-8 UN 2A 0.0021 1.3104 1.2954 - 1.2292 1.2221 1.1616
Int.   2B   1.2020 1.1770   1.2405 1.2313 1.3125
Ext. 15/16-8 UN 3A 0.0000 1.3125 1.2975 - 1.2313 1.2260 1.1637
Int.   3B   1.1922 1.1770   1.2382 1.2313 1.3125
Ext. 15/16-12 UN 2A 0.0017 1.3108 1.2994 - 1.2567 1.2509 1.2116
Int.   2B   1.2400 1.2220   1.2659 1.2584 1.3125
Ext. 15/16-12 UN 3A 0.0000 1.3125 1.3011 - 1.2584 1.2541 1.2133
Int.   3B   1.2323 1.2220   1.2640 1.2584 1.3125
Ext. 15/16-16 UN 2A 0.0015 1.3110 1.3016 - 1.2704 1.2653 1.2365
Int.   2B   1.2590 1.2450   1.2785 1.2719 1.3125
Ext. 15/16-16 UN 3A 0.0000 1.3125 1.3031 - 1.2719 1.2681 1.2380
Int.   3B   1.2533 1.2450   1.2769 1.2719 1.3125
Ext. 15/16-18 UNEF 2A 0.0015 1.3110 1.3023 - 1.2749 1.2700 1.2449
Int.   2B   1.2650 1.2520   1.2827 1.2764 1.3125
Ext. 15/16-18 UNEF 3A 0.0000 1.3125 1.3038 - 1.2764 1.2728 1.2464
Int.   3B   1.2605 1.2520   1.2811 1.2764 1.3125
Ext. 15/16-20 UN 2A 0.0014 1.3111 1.3030 - 1.2786 1.2739 1.2516
Int.   2B   1.2700 1.2580   1.2861 1.2800 1.3125
Ext. 15/16-20 UN 3A 0.0000 1.3125 1.3044 - 1.2800 1.2765 1.2530
Int.   3B   1.2662 1.2580   1.2845 1.2800 1.3125
Ext. 15/16-28 UN 2A 0.0012 1.3113 1.3048 - 1.2881 1.2840 1.2687
Int.   2B   1.2820 1.2740   1.2946 1.2893 1.3125
Ext. 15/16-28 UN 3A 0.0000 1.3125 1.3060 - 1.2893 1.2862 1.2699
Int.   3B   1.2801 1.2740   1.2933 1.2893 1.3125
Ext. 13/8-6 UNC 1A 0.0024 1.3726 1.3453 - 1.2643 1.2523 1.1742
Int.   1B   1.2250 1.1950   1.2822 1.2667 1.3750
Ext. 13/8-6 UNC 2A 0.0024 1.3726 1.3544 1.3453 1.2643 1.2563 1.1742
Int.   2B   1.2250 1.1950   1.2771 1.2667 1.3750
Ext. 13/8-6 UNC 3A 0.0000 1.3750 1.3568 - 1.2667 1.2607 1.1766
Int.   3B   1.2146 1.1950   1.2745 1.2667 1.3750
Ext. 13/8-8 UN 2A 0.0022 1.3728 1.3578 1.3503 1.2916 1.2844 1.2240
Int.   2B   1.2650 1.2400   1.3031 1.2938 1.3750
Ext. 13/8-8 UN 3A 0.0000 1.3750 1.3600 - 1.2938 1.2884 1.2262
Int.   3B   1.2547 1.2400   1.3008 1.2938 1.3750
Ext. 13/8-10 UNS 2A 0.0019 1.3731 1.3602 - 1.3081 1.3018 1.2541
Int.   2B   1.2880 1.2670   1.3182 1.3100 1.3750
Ext. 13/8-12 UNF 1A 0.0019 1.3731 1.3559 - 1.3190 1.3096 1.2739
Int.   1B   1.3030 1.2850   1.3332 1.3209 1.3750
Ext. 13/8-12 UNF 2A 0.0019 1.3731 1.3617 - 1.3190 1.3127 1.2739
Int.   2B   1.3030 1.2850   1.3291 1.3209 1.3750
Ext. 13/8-12 UNF 3A 0.0000 1.3750 1.3636 - 1.3209 1.3162 1.2758
Int.   3B   1.2948 1.2850   1.3270 1.3209 1.3750
Ext. 13/8-14 UNS 2A 0.0016 1.3734 1.3631 - 1.3270 1.3216 1.2884
Int.   2B   1.3140 1.2980   1.3356 1.3286 1.3750
Ext. 13/8-16 UN 2A 0.0015 1.3735 1.3641 - 1.3329 1.3278 1.2990
Int.   2B   1.3210 1.3070   1.3410 1.3344 1.3750
Ext. 13/8-16 UN 3A 0.0000 1.3750 1.3656 - 1.3344 1.3306 1.3005
Int.   3B   1.3158 1.3070   1.3394 1.3344 1.3750
Ext. 13/8-18 UNEF 2A 0.0015 1.3735 1.3648 - 1.3374 1.3325 1.3074
Int.   2B   1.3280 1.3150   1.3452 1.3389 1.3750
Ext. 13/8-18 UNEF 3A 0.0000 1.3750 1.3663 - 1.3389 1.3353 1.3089
Int.   3B   1.3230 1.3150   1.3436 1.3389 1.3750
Ext. 13/8-20 UN 2A 0.0014 1.3736 1.3655 - 1.3411 1.3364 1.3141
Int.   2B   1.3320 1.3210   1.3486 1.3425 1.3750
Ext. 13/8-20 UN 3A 0.0000 1.3750 1.3669 - 1.3425 1.3390 1.3155
Int.   3B   1.3287 1.3210   1.3470 1.3425 1.3750
Ext. 13/8-24 UNS 2A 0.0013 1.3737 1.3665 - 1.3466 1.3423 1.3241
Int.   2B   1.3400 1.3300   1.3535 1.3479 1.3750
Ext. 13/8-28 UN 2A 0.0012 1.3738 1.3673 - 1.3506 1.3465 1.3312
Int.   2B   1.3450 1.3360   1.3571 1.3518 1.3750
Ext. 13/8-28 UN 3A 0.0000 1.3750 1.3685 - 1.3518 1.3487 1.3324
Int.   3B   1.3426 1.3360   1.3558 1.3518 1.3750
Ext. 17/16-6 UN 2A 0.0024 1.4351 1.4169 - 1.3268 1.3188 1.2367
Int.   2B   1.2880 1.2570   1.3396 1.3292 1.4375
Ext. 17/16-6 UN 3A 0.0000 1.4375 1.4193 - 1.3292 1.3232 1.2391
Int.   3B   1.2771 1.2570   1.3370 1.3292 1.4375
Ext. 17/16-8 UN 2A 0.0022 1.4353 1.4203 - 1.3541 1.3469 1.2865
Int.   2B   1.3270 1.3020   1.3657 1.3563 1.4375
Ext. 17/16-8 UN 3A 0.0000 1.4375 1.4225 - 1.3563 1.3509 1.2887
Int.   3B   1.3172 1.3020   1.3634 1.3563 1.4375
Ext. 17/16-12 UN 2A 0.0018 1.4357 1.4243 - 1.3816 1.3757 1.3365
Int.   2B   1.3650 1.3470   1.3910 1.3834 1.4375
Ext. 17/16-12 UN 3A 0.0000 1.4375 1.4261 - 1.3834 1.3790 1.3383
Int.   3B   1.3573 1.3470   1.3891 1.3834 1.4375
Ext. 17/16-16 UN 2A 0.0016 1.4359 1.4265 - 1.3953 1.3901 1.3614
Int.   2B   1.3840 1.3700   1.4037 1.3969 1.4375
Ext. 17/16-16 UN 3A 0.0000 1.4375 1.4281 - 1.3969 1.3930 1.3630
Int.   3B   1.3783 1.3700   1.4020 1.3969 1.4375
Ext. 17/16-18 UNEF 2A 0.0015 1.4360 1.4273 - 1.3999 1.3949 1.3699
Int.   2B   1.3900 1.3770   1.4079 1.4014 1.4375
Ext. 17/16-18 UNEF 3A 0.0000 1.4375 1.4288 - 1.4014 1.3977 1.3714
Int.   3B   1.3855 1.3770   1.4062 1.4014 1.4375
Ext. 17/16-20 UN 2A 0.0014 1.4361 1.4280 - 1.4036 1.3988 1.3766
Int.   2B   1.3950 1.3830   1.4112 1.4050 1.4375
Ext. 17/16-20 UN 3A 0.0000 1.4375 1.4294 - 1.4050 1.4014 1.3780
Int.   3B   1.3912 1.3830   1.4096 1.4050 1.4375
Ext. 17/16-28 UN 2A 0.0013 1.4362 1.4297 - 1.4130 1.4088 1.3936
Int.   2B   1.4070 1.3990   1.4198 1.4143 1.4375
Ext. 17/16-28 UN 3A 0.0000 1.4375 1.4310 - 1.4143 1.4112 1.3949
Int.   3B   1.4051 1.3990   1.4184 1.4143 1.4375
Ext. 11/2-6 UNC 1A 0.0024 1.4976 1.4703 - 1.3893 1.3772 1.2992
Int.   1B   1.3500 1.3200   1.4075 1.3917 1.5000
Ext. 11/2-6 UNC 2A 0.0024 1.4976 1.4794 1.4703 1.3893 1.3812 1.2992
Int.   2B   1.3500 1.3200   1.4022 1.3917 1.5000
Ext. 11/2-6 UNC 3A 0.0000 1.5000 1.4818 - 1.3917 1.3856 1.3016
Int.   3B   1.3396 1.3200   1.3996 1.3917 1.5000
Ext. 11/2-8 UN 2A 0.0022 1.4978 1.4828 1.4753 1.4166 1.4093 1.3490
Int.   2B   1.3900 1.3650   1.4283 1.4188 1.5000
Ext. 11/2-8 UN 3A 0.0000 1.5000 1.4850 - 1.4188 1.4133 1.3512
Int.   3B   1.3797 1.3650   1.4259 1.4188 1.5000
Ext. 11/2-10 UNS 2A 0.0019 1.4981 1.4852 - 1.4331 1.4267 1.3791
Int.   2B   1.4130 1.3920   1.4433 1.4350 1.5000
Ext. 11/2-12 UNF 1A 0.0019 1.4981 1.4809 - 1.4440 1.4344 1.3989
Int.   1B   1.4280 1.4100   1.4584 1.4459 1.5000
Ext. 11/2-12 UNF 2A 0.0019 1.4981 1.4867 - 1.4440 1.4376 1.3989
Int.   2B   1.4280 1.4100   1.4542 1.4459 1.5000
Ext. 11/2-12 UNF 3A 0.0000 1.5000 1.4886 - 1.4459 1.4411 1.4008
Int.   3B   1.4198 1.4100   1.4522 1.4459 1.5000
Ext. 11/2-14 UNS 2A 0.0017 1.4983 1.4880 - 1.4519 1.4464 1.4133
Int.   2B   1.4380 1.4230   1.4608 1.4536 1.5000
Ext. 11/2-16 UN 2A 0.0016 1.4984 1.4890 - 1.4578 1.4526 1.4239
Int.   2B   1.4460 1.4320   1.4662 1.4594 1.5000
Ext. 11/2-16 UN 3A 0.0000 1.5000 1.4906 - 1.4594 1.4555 1.4255
Int.   3B   1.4408 1.4320   1.4645 1.4594 1.5000
Ext. 11/2-18 UNEF 2A 0.0015 1.4985 1.4898 - 1.4624 1.4574 1.4324
Int.   2B   1.4520 1.4400   1.4704 1.4639 1.5000
Ext. 11/2-18 UNEF 3A 0.0000 1.5000 1.4913 - 1.4639 1.4602 1.4339
Int.   3B   1.4480 1.4400   1.4687 1.4639 1.5000
Ext. 11/2-20 UN 2A 0.0014 1.4986 1.4905 - 1.4661 1.4613 1.4391
Int.   2B   1.4570 1.4460   1.4737 1.4675 1.5000
Ext. 11/2-20 UN 3A 0.0000 1.5000 1.4919 - 1.4675 1.4639 1.4405
Int.   3B   1.4537 1.4460   1.4721 1.4675 1.5000
Ext. 11/2-24 UNS 2A 0.0013 1.4987 1.4915 - 1.4716 1.4672 1.4991
Int.   2B   1.4650 1.4550   1.4787 1.4729 1.5000
Ext. 11/2-28 UN 2A 0.0013 1.4987 1.4922 - 1.4755 1.4713 1.4561
Int.   2B   1.4700 1.4610   1.4823 1.4768 1.5000
Ext. 11/2-28 UN 3A 0.0000 1.5000 1.4935 - 1.4768 1.4737 1.4574
Int.   3B   4.4676 1.4610   1.4809 1.4768 1.5000
Ext. 19/16-6 UN 2A 0.0024 1.5601 1.5419 - 1.4518 1.4436 1.3617
Int.   2B   1.4130 1.3820   1.4648 1.4542 1.5625
Ext. 19/16-6 UN 3A 0.0000 1.5625 1.5443 - 1.4542 1.4481 1.3641
Int.   3B   1.4021 1.3820   1.4622 1.4542 1.5625
Ext. 19/16-8 UN 2A 0.0022 1.5603 1.5453 - 1.4791 1.4717 1.4115
Int.   2B   1.4520 1.4270   1.4909 1.4813 1.5625
Ext. 19/16-8 UN 3A 0.0000 1.5625 1.5475 - 1.4813 1.4758 1.4137
Int.   3B   1.4422 1.4270   1.4885 1.4813 1.5625
Ext. 19/16-12 UN 2A 0.0018 1.5607 1.5493 - 1.5066 1.5007 1.4615
Int.   2B   1.4900 1.4720   1.5160 1.5084 1.5625
Ext. 19/16-12 UN 3A 0.0000 1.5625 1.5511 - 1.5084 1.5040 1.4633
Int.   3B   1.4823 1.4720   1.5141 1.5084 1.5625
Ext. 19/16-16 UN 2A 0.0016 1.5609 1.5515 - 1.5203 1.5151 1.4864
Int.   2B   1.5090 1.4950   1.5287 1.5219 1.5625
Ext. 19/16-16 UN 3A 0.0000 1.5625 1.5531 - 1.5219 1.5180 1.4880
Int.   3B   1.5033 1.4950   1.5270 1.5219 1.5625
Ext. 19/16-18 UNEF 2A 0.0015 1.5610 1.5523 - 1.5249 1.5199 1.4949
Int.   2B   1.5150 1.5020   1.5329 1.5264 1.5625
Ext. 19/16-18 UNEF 3A 0.0000 1.5625 1.5538 - 1.5264 1.5227 1.4964
Int.   3B   1.5105 1.5020   1.5312 1.5264 1.5625
Ext. 19/16-20 UN 2A 0.0014 1.5611 1.5530 - 1.5286 1.5238 1.5016
Int.   2B   1.5200 1.5080   1.5362 1.5300 1.5625
Ext. 19/16-20 UN 3A 0.0000 1.5625 1.5544 - 1.5300 1.5264 1.5030
Int.   3B   1.5162 1.5080   1.5346 1.5300 1.5625
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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