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Machine Screw Sizes Threads Per Inch Recommended Tap For Class of Thread Pitch Diameter Limits For Class of Thread Size NC NF Class 2B Class 3B Min. All Classes (Basic) Max Class 2B Max Class 3B 0 1 1 2 2 – 64 – 56 – 80 – 72 – 64 H2 H2 H2 H2 H2 H1 H1 H1 H1 H1 .0519 .0629 .0640 .0744 .0759 .0542 .0655 .0665 .0772 .0786 .0536 .0648 .0659 .0765 .0779 3 3 4 4 5 48 – 40 – 40 – 56 – 48 – H2 H2 H2 H2 H2 H1 H1 H2 H1 H2 .0855 .0874 .0958 .0985 .1088 .0885 .0902 .0991 .1016 .1121 .0877 .0895 .0982 .1008 .1113 5 6 6 8 8 – 32 – 32 – 44 – 40 – 36 H2 H3 H2 H3 H2 H1 H2 H2 H2 H2 .1102 .1177 .1218 .1437 .1460 .1134 .1214 .1252 .1475 .1496 .1126 .1204 .1243 .1465 .1487 10 10 12 12 24 – 24 – – 32 – 28 H3 H3 H3 H3 H3 H2 H3 H3 .1629 .1697 .1889 .1928 .1672 .1736 .1933 .1970 .1661 .1726 .1922 .1959 Fractional Sizes Threads Per Inch Recommended Tap For Class of Thread Pitch Diameter Limits For Class of Thread Size NC NF Class 2B Class 3B Min. All Classes (Basic) Max Class 2B Max Class 3B 1/4 1/4 5/16 5/16 3/8 20 – 18 – 16 – 28 – 24 – H5 *H4 H5 *H4 H5 H3 H3 H3 H3 H3 .2175 .2268 .2764 .2854 .3344 .2223 .2311 .2817 .2902 .3401 .2211 .2300 .2803 .2890 .3387 3/8 7/16 7/16 1/2 1/2 – 14 – 13 – 24 – 20 – 20 *H4 H5 H5 H5 H5 H3 H3 H3 H3 H3 .3479 .3911 .4050 .4500 .4675 .3528 .3972 .4104 .4565 .4731 .3516 .3957 .4091 .4548 .4717 9/16 9/16 5/8 5/8 3/4 12 – 11 – 10 – 18 – 18 – H5 H5 H5 H5 H5 H3 H3 H3 H3 H5 .5084 .5264 .5660 .5889 .6850 .5152 .5323 .5732 .5949 .6927 .5135 .5308 .5714 .5934 .6907 3/4 7/8 7/8 1 1 – 9 – 8 – 16 – 14 – 12 H5 H6 H6 H6 H6 H3 H4 H4 H4 H4 .7094 .8028 .8286 .9188 .9459 .7159 .8110 .8356 .9276 .9535 .7143 .8089 .8339 .9254 .9516		Forming Type Taps Machine Screw and Fractional Sizes Tap Recommendations For Class 2B Fit Tap Recommendations For Class 3B Fit Oversize Forming Taps Tap Size UNC-NF Basic P.D Styles Avail. Max. PD. Thread Limit Styles Avail. Max. PD. Thread Limit Styles Avail. Max. PD. Thread Limit 0-80 1-64 1-72 2-56 2-64 .0519 .0629 .0640 .0744 .0759 – – – H-3 H-3 – – – .0772 .0786 H-2 H-2 H-2 H-2 H-2 .0536 .0648 .0659 .0765 .0779 – – – – – – – – – – 3-48 3-56 4-40 4-48 5-40 .0855 .0874 .0958 .0985 .1088 H-3 H-3 H-5 H-5 H-5 .0885 .0902 .0991 .1016 .1121 H-2 H-2 H-3 H-3 H-3 .0877 .0895 .0982 .1008 .1113 – – – – – – – – – – 5-44 6-32 6-40 8-32 8-36 .1102 .1177 .1218 .1437 .1460 H-5 H-5 H-5 H-5 H-5 .1134 .1214 .1252 .1475 .1496 H-3 H-3 H-3 H-3 H-3 .1126 .1204 .1243 .1465 .1487 – – – – – – – – – – 10-24 10-32 12-24 12-28 1/4-20 .1629 .1697 .1889 .1928 .2175 H-6 H-6 H-6 H-6 H-6 .1672 .1736 .1933 .1970 .2223 H-4 H-4 H-4 H-4 H-4 .1661 .1762 .1922 .1959 .2211 – – – – H-8 – – – – .2215 1/4-28 5/16-18 5/16-24 3/8-16 3/8-24 .2268 .2764 .2854 .3344 .3479 H-6 H-7 H-7 H-7 H-7 .2311 .2817 .2902 .3401 .3528 H-4 H-5 H-5 H-5 H-5 .2300 .2803 .2890 .3387 .3516 H-8 H-9 H-9 H-9 H-9 .2308 .2809 .2899 .3389 .3524 7/16-14 7/16-20 1/2-13 1/2-20 .3911 .4050 .4500 .4675 H-8 H-8 H-8 H-8 .3972 .4104 .4565 .4731 H-5 H-5 H-5 H-5 .3957 .4091 .4548 .4717 – – H-10 H-10 – – .4550 .4725
Metric Sizes For Class 6H Thread Size Internal Thread-Class 6H (Inches) Recommended Tap Minor Dia. Pitch Dia. Nominal Dia. (mm) Pitch (mm) Min. Max. Min. Max. Major Dia. Tap Size Limit Number 1.6 2 2.5 3 3.5 0.35 0.4 0.45 0.5 0.6 .0481 .0617 .0793 .0969 .1123 .0520 .0661 .0841 .1023 .1185 .0541 .0686 .0870 .1054 .1225 .0574 .0720 .0906 .1092 .1268 .0630 .0788 .0985 .1182 .1378 M1.6x0.35 M2 x0.4 M2.5x0.45 M3 x0.5 M3.5x0.6 D-3 D-3 D-3 D-3 D-4 4 4.5 5 6 7 8 0.7 0.75 0.8 1.0 1.0 1.25 .1277 .1452 .1628 .1936 .2330 .2617 .1347 .1526 .1706 .2028 .2422 .2721 .1396 .1580 .1764 .2107 .2500 .2830 .1442 .1626 .1812 .2165 .2559 .2892 .1575 .1772 .1969 .2363 .2756 .3150 M4x0.7 M4.5x0.75 M5x0.8 M6x1 M7x1 M8x1.25 D-4 D-4 D-4 D-5 D-5 D-5 10 12 14 16 1.5 1.75 2.0 2.0 .3298 .3979 .4660 .5447 .3415 .4110 .4807 .5594 .3554 .4277 .5001 .5788 .3624 .4355 .5083 .5871 .3937 .4725 .5512 .6300 M10 x1.5 M12 x1.75 M14 x2 M16 x2 D-6 D-6 D-7 D-7 20 24 30 36 2.5 3.0 3.5 4.0 .6809 .8171 1.0320 1.2469 .6985 .8366 1.0539 1.2704 .7235 .8682 1.0917 1.3151 .7322 .8785 1.1026 1.3268 .7875 .9449 1.1812 1.4174 M20 x2.5 M24 x3 M30 x3.5 M36 x4 D-7 D-8 D-9 D-9