Machinery's Handbook, 31st Edition
Taps
997
Table 19. Taps Sizes for Classes 2B and 3B Unified Screw Threads Machine Screw, Numbered, and Fractional Sizes ANSI/ASME B94.9-2008 (R2018)
Threads per Inch
Recommended Tap For Class of Thread a
Pitch Diameter Limits For Class of Thread
NC UNC
NF UNF
Min., All Classes (Basic)
Max. Class 2B
Max. Class 3B
Size
Class 2B b
Class 3B c
Machine Screw Numbered-Size Taps
0 1 1 2 2 3 3 4 4 5 5 6 6 8 8
… 80 … 72 … 64 … 56 64 56 48 40 … … … … … 48 … 44 … 40 … 36 40 32 32 24 … … … … … 32 … 28 24 …
G H2 G H2 G H2 G H2 G H2 G H2 G H2 G H2 G H2 G H2 G H2 G H3 G H2 G H3 G H2 G H3 G H3 G H3 G H3 G H5 G H4 G H5 G H4 G H5 G H4 G H5 G H5 G H5 G H5 G H5 G H5 G H5 G H5 G H5 G H5 G H6 G H6 G H6 G H6 G H6 G H8 G H6 G H8 G H6 G H8 G H6 G H8 G H6
G H1 G H1 G H1 G H1 G H1 G H1 G H1 G H2 G H1 G H2 G H1 G H2 G H2 G H2 G H2 G H3 G H2 G H3 G H3 G H3 G H3 G H3 G H3 G H3 G H3 G H3 G H3 G H3 G H3 G H3 G H3 G H3 G H3 G H5 G H3 G H4 G H4 G H4 G H4 G H4 G H4 G H4 G H4 G H4 G H4 G H4 G H4 G H4
0.0519 0.0629 0.0640 0.0744 0.0759 0.0855 0.0874 0.0958 0.0985 0.1088 0.1102 0.1177 0.1218 0.1437 0.1460 0.1629 0.1697 0.1889 0.1928 0.2175 0.2268 0.2764 0.2854 0.3344 0.3479 0.3911 0.4050 0.4500 0.4675 0.5084 0.5264 0.5660 0.5889 0.6850 0.7094 0.8028 0.8286 0.9188 0.9459 0.9536 1.0322 1.0709 1.1572 1.1959 1.2667 1.3209 1.3917 1.4459
0.0542 0.0655 0.0665 0.0772 0.0786 0.0885 0.0902 0.0991 0.1016 0.1121 0.1134 0.1214 0.1252 0.1475 0.1496 0.1672 0.1736 0.1933 0.1970 0.2224 0.2311 0.2817 0.2902 0.3401 0.3528 0.3972 0.4104 0.4565 0.4731 0.5152 0.5323 0.5732 0.5949 0.6927 0.7159 0.8110 0.8356 0.9276 0.9535 0.9609 1.0416 1.0787 1.1668 1.2039 1.2771 1.3291 1.4022 1.4542
0.0536 0.0648 0.0659 0.0765 0.0779 0.0877 0.0895 0.0982 0.1008 0.1113 0.1126 0.1204 0.1243 0.1465 0.1487 0.1661 0.1726 0.1922 0.1959 0.2211 0.2300 0.2803 0.2890 0.3387 0.3516 0.3957 0.4091 0.4548 0.4717 0.5135 0.5308 0.5714 0.5934 0.6907 0.7143 0.8089 0.8339 0.9254 0.9516 0.9590 1.0393 1.0768 1.1644 1.2019 1.2745 1.3270 1.3996 1.4522
10 10 12 12
Fractional-Size Taps
20
…
1 ⁄ 4 1 ⁄ 4
… 28
18
…
5 ⁄ 16 5 ⁄ 16
… 24
16
…
3 ⁄ 8 3 ⁄ 8
… 24
14
…
7 ⁄ 16 7 ⁄ 16
… 20
13
…
1 ⁄ 2 1 ⁄ 2
… 20
12
…
9 ⁄ 16 9 ⁄ 16
… 18
11
…
5 ⁄ 8 5 ⁄ 8 3 ⁄ 4 3 ⁄ 4 7 ⁄ 8 7 ⁄ 8
… 18
10
…
… 16
9
…
… 14 … 12 8 …
1 1
1 14NS 14NS
7
…
1 1 ⁄ 8 1 1 ⁄ 8 1 1 ⁄ 4 1 1 ⁄ 4 1 3 ⁄ 8 1 3 ⁄ 8 1 1 ⁄ 2 1 1 ⁄ 2
… 12
7
…
… 12
6
…
… 12
6
…
… 12
a Recommended taps are for cutting threads only and are not for roll-form threads. b Cut-thread taps in sizes #3 to 1 1 ⁄ conditions and in average materials for producing Class 2B tapped holes. c Taps suited for class 3B are satisfactory for class 2B threads. All dimensions are given in inches. The above recommended taps normally produce the class of thread indicated in average materials when used with reasonable care. However, if the tap specified does not give a satisfactory gage fit in the work, a choice of some other limit tap will be necessary. 2 in. NC and NF, inclusive, may be used under all normal
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