Thread Limits Machine Screw Taps - Ground Thread Unified and American National Form (USCTI Table 329)
LEAD TOLERANCE A maximum lead deviation of plus or minus 0.0005” within any two threads not farther apart than one inch is permitted. ANGLE TOLERANCE 6 to 9 threads per inch incl. = ± 25’ in 1/2 angle. 10 to 80 threads per inch incl., = ± 30’ in 1/2 angle. FORMULA Maximum major diameter = Basic +A. Minimum major diameter = Basic +B. For values of A and B see table 331. PITCH DIAMETER LIMITS FOR TAPS THROUGH 1” DIAMETER H1 Limit = Basic PD to basic PD + 0.0005”. H2 Limit = Basic PD + 0.0005” to Basic PD + 0.0010”. H3 Limit = Basic PD + 0.0010” to Basic PD + 0.0015”. H4 Limit = Basic PD + 0.0015” to Basic PD + 0.0020”. H5 Limit = Basic PD + 0.0020” to Basic PD + 0.0025”. H6 Limit = Basic PD + 0.0025” to Basic PD + 0.0030”. PITCH DIAMETER LIMITS FOR TAPS OVER 1” DIAMETER THROUGH 1-1/2” DIAMETER H4 Limit = Basic PD + 0.0010” to Basic PD + 0.0020”.
Threads Per Inch
Major Diameter
Pitch Diameter Limits
Tap Size (Inch)
Basic Pitch Dia.
H1 Limit H7 Limit* Min. Max. Min. Max. Min. Max. Min. Max. H2 Limit H3 Limit
NC UNC
UF UNF
NS Basic Min. Max.
0 – 80 – 0.0600 0.0605 0.0616 0.0519 0.0519 0.0524 0.0524 0.0529 – – – – 1 64 – – 0.0730 0.0736 0.0750 0.0629 0.0629 0.0634 0.0634 0.0639 – – – – 1 – 72 – 0.0730 0.0736 0.0748 0.0640 0.0640 0.0645 0.0645 0.0650 – – – – 2 56 – – 0.0860 0.0867 0.0883 0.0744 0.0744 0.0749 0.0749 0.0754 – – – – 2 – 64 – 0.0860 0.0866 0.0880 0.0759 0.0759 0.0764 0.0764 0.0769 – – – – 3 48 – – 0.0990 0.0999 0.1017 0.0855 0.0855 0.0860 0.0860 0.0865 – – – – 3 – 56 – 0.0990 0.0997 0.1013 0.0874 0.0874 0.0879 0.0879 0.0884 – – – – 4 – – 36 0.1120 0.1135 0.1156 0.0940 – – 0.0945 0.0950 – – – – 4 40 – – 0.1120 0.1133 0.1152 0.0958 0.0958 0.0963 0.0963 0.0968 – – – – 4 – 48 – 0.1120 0.1129 0.1147 0.0985 0.0985 0.0990 0.0990 0.0995 – – – – 5 40 – – 0.1250 0.1263 0.1282 0.1088 0.1088 0.1093 0.1093 0.1098 – – – – 5 – 44 – 0.1250 0.1263 0.1280 0.1102 – – 0.1107 0.1112 – – – – 6 32 – – 0.1380 0.1401 0.1421 0.1177 0.1177 0.1182 0.1182 0.1187 0.1187 0.1192 0.1207 0.1212 6 – 40 – 0.1380 0.1393 0.1412 0.1218 0.1218 0.1223 0.1223 0.1228 – – – – 8 32 – – 0.1640 0.1661 0.1681 0.1437 0.1437 0.1442 0.1442 0.1447 0.1447 0.1452 0.1467 0.1472 8 – 36 – 0.1640 0.1655 0.1676 0.1460 0.1460 0.1465 0.1465 0.1470 – – – – 10 24 – – 0.1900 0.1927 0.1954 0.1629 0.1629 0.1634 0.1634 0.1639 0.1639 0.1644 0.1659 0.1664 10 – 32 – 0.1900 0.1921 0.1941 0.1697 0.1697 0.1702 0.1702 0.1707 0.1707 0.1712 0.1727 0.1732 12 24 – – 0.2160 0.2187 0.2214 0.1889 0.1889 0.1894 – – 0.1899 0.1904 – – 12 – 28 – 0.2160 0.2183 0.2206 0.1928 0.1928 0.1933 – – 0.1938 0.1943 – – *Major diameter for H7 Limit Taps is 0.002” larger than values shown in min. and max. columns.
Fractional Size Taps - Ground Thread Unified and Americal National Form (USCTI Table 327)
Threads Per Inch
Major Diameter
Pitch Diameter Limits
Tap Size (Inch)
Basic Pitch Dia.
H1 Limit
H2 Limit
H3 Limit
H4 Limit
H5 Limit
H6 Limit
NC UNC
UF UNF
NS Basic Min.
Max.
Min.
Max.
Min.
Max.
Min.
Max.
Min.
Max.
Min.
Max.
Min.
Max.
1/4
20 – – 0.2500 0.2533 0.2565 0.2175 0.2175 0.2180 0.2180 0.2185 0.2185 0.2190 –
– 0.2195 0.2200
–
–
1/4 – 28 – 0.2500 0.2523 0.2546 0.2268 0.2268 0.2273 0.2273 0.2278 0.2278 0.2283 0.2283 0.2288 – – – – 5/16 18 – – 0.3125 0.3161 0.3197 0.2764 0.2764 0.2769 0.2769 0.2774 0.2774 0.2779 – – 0.2784 0.2789 – – 5/16 – 24 – 0.3125 0.3152 0.3179 0.2854 0.2854 0.2859 0.2859 0.2864 0.2864 0.2869 0.2869 0.2874 – – – – 3/8 16 – – 0.3750 0.3790 0.3831 0.3344 0.3344 0.3349 0.3349 0.3354 0.3354 0.3359 – – 0.3364 0.3369 – – 3/8 – 24 – 0.3750 0.3777 0.3804 0.3479 0.3479 0.3484 0.3484 0.3489 0.3489 0.3494 0.3494 0.3499 – – – – 7/16 14 – – 0.4375 0.4422 0.4468 0.3911 0.3911 0.3916 0.3916 0.3921 0.3921 0.3926 – – 0.3931 0.3936 – – 7/16 – 20 – 0.4375 0.4408 0.4440 0.4050 0.4050 0.4055 0.4055 0.4060 0.4060 0.4065 – – 0.4070 0.4075 – – 1/2 13 – – 0.5000 0.5050 0.5100 0.4500 0.4500 0.4505 0.4505 0.4510 0.4510 0.4515 – – 0.4520 0.4525 – – 1/2 – 20 – 0.5000 0.5033 0.5065 0.4675 0.4675 0.4680 0.4680 0.4685 0.4685 0.4690 – – 0.4695 0.4700 – – 9/16 12 – – 0.5625 0.5679 0.5733 0.5084 0.5084 0.5089 0.5089 0.5094 0.5094 0.5099 – – 0.5104 0.5109 – – 9/16 – 18 – 0.5625 0.5661 0.5697 0.5264 0.5264 0.5269 0.5269 0.5274 0.5274 0.5279 – – 0.5284 0.5289 – – 5/8 11 – – 0.6250 0.6309 0.6368 0.5660 0.5660 0.5665 0.5665 0.5670 0.5670 0.5675 – – 0.5680 0.5685 – – 5/8 – 18 – 0.6250 0.6286 0.6322 0.5889 0.5889 0.5894 0.5894 0.5899 0.5899 0.5904 – – 0.5909 0.5914 – – 11/16 – – 11 0.6875 0.6934 0.6993 0.6285 – – – – 0.6295 0.6300 – – – – – – 11/16 – – 16 0.6875 0.6915 0.6956 0.6469 – – – – 0.6479 0.6484 – – – – – – 3/4 10 – – 0.7500 0.7565 0.7630 0.6850 0.6850 0.6855 0.6855 0.6860 0.6860 0.6865 – 0.8048 0.6870 0.6875 – – 3/4 – 16 – 0.7500 0.7540 0.7581 0.7094 0.7094 0.7099 0.7099 0.7104 0.7104 0.7109 – 0.8306 0.7114 0.7119 – – 7/8 9 – – 0.8750 0.8822 0.8894 0.8028 0.8028 0.8033 0.8033 0.8038 – – 0.8043 0.9208 – – 0.8053 0.8058 7/8 – 14 – 0.8750 0.8797 0.8843 0.8286 0.8286 0.8291 0.8291 0.8296 – – 0.8301 0.9479 – – 0.8311 0.8316 1 8 – – 1.0000 1.0081 1.0162 0.9188 0.9188 0.9193 0.9193 0.9198 – – 0.9203 0.9556 – – 0.9213 0.9218 1 – 12 – 1.0000 1.0054 1.0108 0.9459 – – – – – – 0.9474 1.0342 – – – – 1 – – 14 1.0000 1.0047 1.0093 0.9536 – – 0.9541 0.9546 – – 0.9551 1.0729 – – 0.9561 0.9566 1 1/8 7 – – 1.1250 1.1343 1.1436 1.0322 – – – – – – 1.0332 1.1592 – – – – 1 1/8 – 12 – 1.1250 1.1304 1.1358 1.0709 – – – – – – 1.0719 1.1979 – – – – 1 1/4 7 – – 1.2500 1.2593 1.2686 1.1572 – – – – – – 1.1582 1.2687 – – – – 1 1/4 – 12 – 1.2500 1.2554 1.2608 1.1959 – – – – – – 1.1969 1.3229 – – – – 1 3/8 6 – – 1.3750 1.3859 1.3967 1.2667 – – – – – – 1.2677 1.3937 – – – – 1 3/8 – 12 – 1.3750 1.3804 1.3858 1.3209 – – – – – – 1.3219 1.4479 – – – – 1 1/2 6 – – 1.5000 1.5109 1.5217 1.3917 – – – – – – 1.3927 – – – – – 1 1/2 – 12 – 1.5000 1.5054 1.5108 1.4459 – – – – – – 1.4469 – – – – –
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