Taps Table 23. Tap Thread Limits: Fractional Sizes, Cut Thread ANSI/ASME B94.9-2008 (R2018) (Unified and American National Thread Forms) Threads per Inch Major Diameter Pitch Diameter Size NC UNC NF UNF NS UNS Basic Min. Max. Basic Min. Max. 1 ⁄ 8 … … 40 0.1250 0.1266 0.1286 0.1088 0.1090 0.1105 5 ⁄ 32 … … 32 0.1563 0.1585 0.1605 0.13595 0.13645 0.1380 3 ⁄ 16 … … 24 0.1875 0.1903 0.1923 0.1604 0.1609 0.1624 3 ⁄ 16 … … 32 0.1875 0.1897 0.1917 0.1672 0.1677 0.1692 1 ⁄ 4 20 … … 0.2500 0.2532 0.2557 0.2175 0.2180 0.2200 1 ⁄ 4 … 28 … 0.2500 0.2524 0.2549 0.2268 0.2273 0.2288 5 ⁄ 16 18 … … 0.3125 0.3160 0.3185 0.2764 0.2769 0.2789 5 ⁄ 16 … 24 … 0.3125 0.3153 0.3178 0.2854 0.2859 0.2874 3 ⁄ 8 16 … … 0.3750 0.3789 0.3814 0.3344 0.3349 0.3369 3 ⁄ 8 … 24 … 0.3750 0.3778 0.3803 0.3479 0.3484 0.3499 7 ⁄ 16 14 … … 0.4375 0.4419 0.4449 0.3911 0.3916 0.3941 7 ⁄ 16 … 20 … 0.4375 0.4407 0.4437 0.4050 0.4055 0.4075 1 ⁄ 2 13 … … 0.5000 0.5047 0.5077 0.4500 0.4505 0.4530 1 ⁄ 2 … 20 … 0.5000 0.5032 0.5062 0.4675 0.4680 0.4700 9 ⁄ 16 12 … … 0.5625 0.5675 0.5705 0.5084 0.5089 0.5114 9 ⁄ 16 … 18 … 0.5625 0.5660 0.5690 0.5264 0.5269 0.5289 5 ⁄ 8 11 … … 0.6250 0.6304 0.6334 0.5660 0.5665 0.5690 5 ⁄ 8 … 18 … 0.6250 0.6285 0.6315 0.5889 0.5894 0.5914 3 ⁄ 4 10 … … 0.7500 0.7559 0.7599 0.6850 0.6855 0.6885 3 ⁄ 4 … 16 … 0.7500 0.7539 0.7579 0.7094 0.7099 0.7124 7 ⁄ 8 9 … … 0.8750 0.8820 0.8860 0.8028 0.8038 0.8068 7 ⁄ 8 … 14 … 0.8750 0.8799 0.8839 0.8286 0.8296 0.8321 1 8 … … 1.0000 1.0078 1.0118 0.9188 0.9198 0.9228 1 … 12 … 1.0000 1.0055 1.0095 0.9459 0.9469 0.9494 1 … … 14 1.0000 1.0049 1.0089 0.9536 0.9546 0.9571 1 1 ⁄ 8 7 … … 1.1250 1.1337 1.1382 1.0322 1.0332 1.0367 1 1 ⁄ 8 … 12 … 1.1250 1.1305 1.1350 1.0709 1.0719 1.0749 1 1 ⁄ 4 7 … … 1.2500 1.2587 1.2632 1.1572 1.1582 1.1617 1 1 ⁄ 4 … 12 … 1.2500 1.2555 1.2600 1.1959 1.1969 1.1999 1 3 ⁄ 8 6 … … 1.3750 1.3850 1.3895 1.2667 1.2677 1.2712 1 3 ⁄ 8 … 12 … 1.3750 1.3805 1.3850 1.3209 1.3219 1.3249 1 1 ⁄ 2 6 … … 1.5000 1.5100 1.5145 1.3917 1.3927 1.3962 1 1 ⁄ 2 … 12 … 1.5000 1.5055 1.5100 1.4459 1.4469 1.4499 1 3 ⁄ 4 5 … … 1.7500 1.7602 1.7657 1.6201 1.6216 1.6256 2 4.5 … … 2.0000 2.0111 2.0166 1.8557 1.8572 1.8612 Threads per Inch Half Angle Full Angle 4 1 ⁄ 2 to 5 1 ⁄ 2 ±0 ° 35 ′ ±0 ° 53 ′ 6 to 9 ±0 ° 40 ′ ±0 ° 60 ′ 10 to 28 ±0 ° 45 ′ ±0 ° 68 ′ 30 to 64 ±0 ° 60 ′ ±0 ° 90 ′ A maximum lead error of ± 0.003 inch in 1 inch of thread is permitted. All dimensions are given in inches. Thread limits are computed from Table 3. Machinery's Handbook, 31st Edition
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