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. 5/16-18 UNC 1A 0.0012 0.3113 0.2982 - 0.2752 0.2691 0.2452
Int.   1B   0.2650 0.2520   0.2843 0.2764 0.3125
Ext. 5/16-18 UNC 2A 0.0012 0.3113 0.3026 0.2982 0.2752 0.2712 0.2452
Int.   2B   0.2650 0.2520   0.2817 0.2764 0.3125
Ext. 5/16-18 UNC 3A 0.0000 0.3125 0.3038 - 0.2764 0.2734 0.2464
Int.   3B   0.2630 0.2520   0.2803 0.2764 0.3125
Ext. 5/16-20 UN 2A 0.0012 0.3113 0.3032 - 0.2788 0.2748 0.2518
Int.   2B   0.2700 0.2580   0.2852 0.2800 0.3125
Ext. 5/16-20 UN 3A 0.0000 0.3125 0.3044 - 0.2800 0.2770 0.2530
Int.   3B   0.2680 0.2580   0.2839 0.2800 0.3125
Ext. 5/16-24 UNF 1A 0.0011 0.3114 0.3006 - 0.2843 0.2788 0.2618
Int.   1B   0.2770 0.2670   0.2925 0.2854 0.3125
Ext. 5/16-24 UNF 2A 0.0011 0.3114 0.3042 - 0.2843 0.2806 0.2618
Int.   2B   0.2770 0.2670   0.2902 0.2854 0.3125
Ext. 5/16-24 UNF 3A 0.0000 0.3125 0.3053 - 0.2854 0.2827 0.2629
Int.   3B   0.2754 0.2670   0.2890 0.2854 0.3125
Ext. 5/16-27 UNS 2A 0.0010 0.3115 0.3048 - 0.2874 0.2839 0.2674
Int.   2B   0.2810 0.2720   0.2929 0.2884 0.3125
Ext. 5/16-28 UN 2A 0.0010 0.3115 0.3050 - 0.2883 0.2849 0.2689
Int.   2B   0.2820 0.2740   0.2937 0.2893 0.3125
Ext. 5/16-28 UN 3A 0.0000 0.3125 0.3060 - 0.2893 0.2867 0.2699
Int.   3B   0.2807 0.2740   0.2926 0.2893 0.3125
Ext. 5/16-32 UNEF 2A 0.0010 0.3115 0.3055 - 0.2912 0.2880 0.2743
Int.   2B   0.2860 0.2790   0.2964 0.2922 0.3125
Ext. 5/16-32 UNEF 3A 0.0000 0.3125 0.3065 - 0.2922 0.2898 0.2753
Int.   3B   0.2847 0.2790   0.2953 0.2922 0.3125
Ext. 5/16-36 UNS 2A 0.0009 0.3116 0.3061 - 0.2936 0.2905 0.2785
Int.   2B   0.2890 0.2820   0.2985 0.2945 0.3125
Ext. 5/16-40 UNS 2A 0.0009 0.3116 0.3065 - 0.2954 0.2925 0.2818
Int.   2B   0.2910 0.2850   0.3001 0.2963 0.3125
Ext. 5/16-48 UNS 2A 0.0008 0.3117 0.3072 - 0.2982 0.2955 0.2869
Int.   2B   0.2950 0.2900   0.3026 0.2990 0.3125
Ext. 3/8-16 UNC 1A 0.0013 0.3737 0.3595 - 0.3331 0.3266 0.2992
Int.   1B   0.3210 0.3070   0.3429 0.3344 0.3750
Ext. 3/8-16 UNC 2A 0.0013 0.3737 0.3643 0.3595 0.3331 0.3287 0.2992
Int.   2B   0.3210 0.3070   0.3401 0.3344 0.3750
Ext. 3/8-16 UNC 3A 0.0000 0.3750 0.3656 - 0.3344 0.3311 0.3005
Int.   3B   0.3182 0.3070   0.3387 0.3344 0.3750
Ext. 3/8-18 UNS 2A 0.0013 0.3737 0.3650 - 0.3376 0.3333 0.3076
Int.   2B   0.3280 0.3150   0.3445 0.3389 0.3750
Ext. 3/8-20 UN 2A 0.0012 0.3738 0.3657 - 0.3413 0.3372 0.3143
Int.   2B   0.3320 0.3210   0.3479 0.3425 0.3750
Ext. 3/8-20 UN 3A 0.0000 0.3750 0.3669 - 0.3425 0.3394 0.3155
Int.   3B   0.3297 0.3210   0.3465 0.3425 0.3750
Ext. 3/8-24 UNF 1A 0.0011 0.3739 0.3631 - 0.3468 0.3411 0.3243
Int.   1B   0.3400 0.3300   0.3553 0.3479 0.3750
Ext. 3/8-24 UNF 2A 0.0011 0.3739 0.3667 - 0.3468 0.3430 0.3243
Int.   2B   0.3400 0.3300   0.3528 0.3479 0.3750
Ext. 3/8-24 UNF 3A 0.0000 0.3750 0.3678 - 0.3479 0.3450 0.3254
Int.   3B   0.3372 0.3300   0.3516 0.3479 0.3750
Ext. 3/8-27 UNS 2A 0.0011 0.3739 0.3672 - 0.3498 0.3462 0.3298
Int.   2B   0.3440 0.3350   0.3556 0.3509 0.3750
Ext. 3/8-28 UN 2A 0.0011 0.3739 0.3674 - 0.3507 0.3471 0.3313
Int.   2B   0.3450 0.3360   0.3564 0.3518 0.3750
Ext. 3/8-28 UN 3A 0.0000 0.3750 0.3685 - 0.3518 0.3491 0.3324
Int.   3B   0.3426 0.3360   0.3553 0.3518 0.3750
Ext. 3/8-32 UNEF 2A 0.0010 0.3740 0.3680 - 0.3537 0.3503 0.3368
Int.   2B   0.3490 0.3410   0.3591 0.3547 0.3750
Ext. 3/8-32 UNEF 3A 0.0000 0.3750 0.3690 - 0.3547 0.3522 0.3378
Int.   3B   0.3469 0.3410   0.3580 0.3547 0.3750
Ext. 3/8-36 UNS 2A 0.0010 0.3740 0.3685 - 0.3560 0.3528 0.3409
Int.   2B   0.3520 0.3450   0.3612 0.3570 0.3750
Ext. 3/8-40 UNS 2A 0.0009 0.3741 0.3690 - 0.3579 0.3548 0.3443
Int.   2B   0.3540 0.3480   0.3628 0.3588 0.3750
Ext. 0.390—27 UNS 2A 0.0011 0.3889 0.3822 - 0.3648 0.3612 0.3448
Int.   2B   0.3590 0.3500   0.3706 0.3659 0.3900
Ext. 7/16-14 UNC 1A 0.0014 0.4361 0.4206 - 0.3897 0.3826 0.3511
Int.   1B   0.3760 0.3600   0.4003 0.3911 0.4375
Ext. 7/16-14 UNC 2A 0.0014 0.4361 0.4258 0.4206 0.3897 0.3850 0.3511
Int.   2B   0.3760 0.3600   0.3972 0.3911 0.4375
Ext. 7/16-14 UNC 3A 0.0000 0.4375 0.4272 - 0.3911 0.3876 0.3525
Int.   3B   0.3717 0.3600   0.3957 0.3911 0.4375
Ext. 7/16-16 UN 2A 0.0014 0.4361 0.4267 - 0.3955 0.3909 0.3616
Int.   2B   0.3840 0.3700   0.4028 0.3969 0.4375
Ext. 7/16-16 UN 3A 0.0000 0.4375 0.4281 - 0.3969 0.3935 0.3630
Int.   3B   0.3800 0.3700   0.4014 0.3969 0.4375
Ext. 7/16-18 UNS 2A 0.0013 0.4362 0.4275 - 0.4001 0.3958 0.3701
Int.   2B   0.3900 0.3770   0.4070 0.4014 0.4375
Ext. 7/16-20 UNF 1A 0.0013 0.4362 0.4240 - 0.4037 0.3975 0.3767
Int.   1B   0.3950 0.3830   0.4131 0.4050 0.4375
Ext. 7/16-20 UNF 2A 0.0013 0.4362 0.4281 - 0.4037 0.3995 0.3767
Int.   2B   0.3950 0.3830   0.4104 0.4050 0.4375
Ext. 7/16-20 UNF 3A 0.0000 0.4375 0.4294 - 0.4050 0.4019 0.3780
Int.   3B   0.3916 0.3830   0.4091 0.4050 0.4375
Ext. 7/16-24 UNS 2A 0.0011 0.4364 0.4292 - 0.4093 0.4055 0.3868
Int.   2B   0.4020 0.3920   0.4153 0.4104 0.4375
Ext. 7/16-27 UNS 2A 0.0011 0.4364 0.4297 - 0.4123 0.4087 0.3923
Int.   2B   0.4060 0.3970   0.4181 0.4134 0.4375
Ext. 7/16-28 UNEF 2A 0.0011 0.4364 0.4299 - 0.4132 0.4096 0.3838
Int.   2B   0.4070 0.3990   0.4189 0.4143 0.4375
Ext. 7/16-28 UNEF 3A 0.0000 0.4375 0.4310 - 0.4143 0.4116 0.3949
Int.   3B   0.4051 0.3990   0.4178 0.4143 0.4375
Ext. 7/16-32 UN 2A 0.0010 0.4365 0.4305 - 0.4162 0.4128 0.3993
Int.   2B   0.4110 0.4040   0.4216 0.4172 0.4375
Ext. 7/16-32 UN 3A 0.0000 0.4375 0.4315 - 0.4172 0.4147 0.4003
Int.   3B   0.4094 0.4040   0.4205 0.4172 0.4375
Ext. 1/2-12 UNS 2A 0.0016 0.4984 0.4870 - 0.4443 0.4389 0.3992
Int.   2B   0.4280 0.4100   0.4529 0.4459 0.5000
Ext. 1/2-12 UNS 3A 0.0000 0.5000 0.4886 - 0.4459 0.4419 0.4008
Int.   3B   0.4223 0.4100   0.4511 0.4459 0.5000
Ext. 1/2-13 UNC 1A 0.0015 0.4985 0.4822 - 0.4485 0.4411 0.4069
Int.   1B   0.4340 0.4170   0.4597 0.4500 0.5000
Ext. 1/2-13 UNC 2A 0.0015 0.4985 0.4876 0.4822 0.4485 0.4435 0.4069
Int.   2B   0.4340 0.4170   0.4565 0.4500 0.5000
Ext. 1/2-13 UNC 3A 0.0000 0.5000 0.4891 - 0.4500 0.4463 0.4084
Int.   3B   0.4284 0.4170   0.4548 0.4500 0.5000
Ext. 1/2-14 UNS 2A 0.0015 0.4985 0.4882 - 0.4521 0.4471 0.4135
Int.   2B   0.4380 0.4230   0.4601 0.4536 0.5000
Ext. 1/2-16 UN 2A 0.0000 0.4986 0.4892 - 0.4580 0.4533 0.4241
Int.   2B   0.4460 0.4320   0.4655 0.4594 0.5000
Ext. 1/2-16 UN 3A 0.0000 0.5000 0.4906 - 0.4594 0.4559 0.4255
Int.   3B   0.4419 0.4320   0.4640 0.4594 0.5000
Ext. 1/2-18 UNS 2A 0.0013 0.4987 0.4900 - 0.4626 0.4582 0.4326
Int.   2B   0.4530 0.4400   0.4697 0.4639 0.5000
Ext. 1/2-20 UNF 1A 0.0013 0.4987 0.4865 - 0.4662 0.4598 0.4392
Int.   1B   0.4570 0.4460   0.4759 0.4675 0.5000
Ext. 1/2-20 UNF 2A 0.0013 0.4987 0.4906 - 0.4662 0.4619 0.4392
Int.   2B   0.4570 0.4460   0.4731 0.4675 0.5000
Ext. 1/2-20 UNF 3A 0.0000 0.5000 0.4919 - 0.4675 0.4643 0.4405
Int.   3B   0.4537 0.4460   0.4717 0.4675 0.5000
Ext. 1/2-24 UNS 2A 0.0012 0.4988 0.4916 - 0.4717 0.4678 0.4492
Int.   2B   0.4650 0.4550   0.4780 0.4729 0.5000
Ext. 1/2-27 UNS 2A 0.0011 0.4989 0.4922 - 0.4748 0.4711 0.4548
Int.   2B   0.4690 0.4600   0.4807 0.4759 0.5000
Ext. 1/2-28 UNEF 2A 0.0011 0.4989 0.4924 - 0.4757 0.4720 0.4563
Int.   2B   0.4700 0.4610   0.4816 0.4768 0.5000
Ext. 1/2-28 UNEF 3A 0.0000 0.5000 0.4935 - 0.4768 0.4740 0.4574
Int.   3B   0.4676 0.4610   0.4804 0.4768 0.5000
Ext. 1/2-32 UN 2A 0.0010 0.4990 0.4930 - 0.4787 0.4752 0.4618
Int.   2B   0.4740 0.4660   0.4842 0.4797 0.5000
Ext. 1/2-32 UN 3A 0.0000 0.5000 0.4940 - 0.4797 0.4771 0.4628
Int.   3B   0.4719 0.4660   0.4831 0.4797 0.5000
Ext. 9/16-12 UNC 1A 0.0016 0.5609 0.5437 - 0.5068 0.4990 0.4617
Int.   1B   0.4900 0.4720   0.5186 0.5084 0.5625
Ext. 9/16-12 UNC 2A 0.0016 0.5609 0.5495 0.5437 0.5068 0.5016 0.4617
Int.   2B   0.4900 0.4720   0.5152 0.5084 0.5625
Ext. 9/16-12 UNC 3A 0.0000 0.5625 0.5511 - 0.5084 0.5045 0.4633
Int.   3B   0.4843 0.4720   0.5135 0.5084 0.5625
Ext. 9/16-14 UNS 2A 0.0015 0.5610 0.5507 - 0.5146 0.5096 0.4760
Int.   2B   0.5010 0.4850   0.5226 0.5161 0.5625
Ext. 9/16-16 UN 2A 0.0014 0.5611 0.5517 - 0.5205 0.5158 0.4866
Int.   2B   0.5090 0.4950   0.5280 0.5219 0.5625
Ext. 9/16-16 UN 3A 0.0000 0.5625 0.5531 - 0.5219 0.5184 0.4880
Int.   3B   0.5040 0.4950   0.5265 0.5219 0.5625
Ext. 9/16-18 UNF 1A 0.0014 0.5611 0.5480 - 0.5250 0.5182 0.4950
Int.   1B   0.5150 0.5020   0.5353 0.5264 0.5625
Ext. 9/16-18 UNF 2A 0.0014 0.5611 0.5524 - 0.5250 0.5205 0.4950
Int.   2B   0.5150 0.5020   0.5323 0.5264 0.5625
Ext. 9/16-18 UNF 3A 0.0000 0.5625 0.5538 - 0.5264 0.5230 0.4964
Int.   3B   0.5106 0.5020   0.5308 0.5264 0.5625
Ext. 9/16-20 UN 2A 0.0013 0.5612 0.5531 - 0.5287 0.5245 0.5017
Int.   2B   0.5200 0.5080   0.5355 0.5300 0.5625
Ext. 9/16-20 UN 3A 0.0000 0.5625 0.5544 - 0.5300 0.5268 0.5030
Int.   3B   0.5162 0.5080   0.5341 0.5300 0.5625
Ext. 9/16-24 UNEF 2A 0.0012 0.5613 0.5541 - 0.5342 0.5303 0.5117
Int.   2B   0.5270 0.5170   0.5405 0.5354 0.5625
Ext. 9/16-24 UNEF 3A 0.0000 0.5625 0.5553 - 0.5354 0.5325 0.5129
Int.   3B   0.5244 0.5170   0.5392 0.5354 0.5625
Ext. 9/16-27 UNS 2A 0.0011 0.5614 0.5547 - 0.5373 0.5336 0.5173
Int.   2B   0.5310 0.5220   0.5432 0.5384 0.5625
Ext. 9/16-28 UN 2A 0.0011 0.5614 0.5549 - 0.5382 0.5345 0.5188
Int.   2B   0.5320 0.5240   0.5441 0.5393 0.5625
Ext. 9/16-28 UN 3A 0.0000 0.5625 0.5560 - 0.5393 0.5365 0.5199
Int.   3B   0.5301 0.5240   0.5429 0.5393 0.5625
Ext. 9/16-32 UN 2A 0.0010 0.5615 0.5555 - 0.5412 0.5377 0.5243
Int.   2B   0.5360 0.5290   0.5467 0.5422 0.5625
Ext. 9/16-32 UN 3A 0.0000 0.5625 0.5565 - 0.5422 0.5396 0.5253
Int.   3B   0.5344 0.5290   0.5456 0.5422 0.5625
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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