Machinery's Handbook, 31st Edition
Taps 987 Table 7. Machine Screw and Fractional Size Ground Thread Dimensions for Screw Thread Insert (STI) Taps ANSI/ASME B94.9-2008 (R2018)
Threads per inch
Tap Dimensions, inch
Nominal Size (STI)
Blank Design No.
Table 5a Blank Equivalent (Reference)
Overall length, L
Thread Length, I
Square Length, I 2
Shank Diameter, d 1
Size of Square, a
NC
NF
1 2 3 4 5 6
64 56 48 40 40 32 32 24 24 20 18 16
… 64 56 48 … … 36 32 … 28 24 …
1 1 1 1 1 1 1 1 2 2 2 2 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3
1.81 1.88 1.94 2.00 2.13 2.38 2.13 2.38 2.50 2.72 2.72 2.94 3.38 3.16 3.59 3.38 3.81 3.59 4.03 3.81 4.25 4.03 4.69 4.47 5.13 5.75 5.44 6.06 5.75 6.38 6.06 6.69 6.38 7.00 6.69
0.50 0.56 0.63 0.69 0.75 0.88 0.75 0.94 1.00 1.13 1.13 1.25 1.66 1.44 1.66 1.66 1.81 1.66 1.81 1.81 2.00 1.81 2.22 2.00 2.50 2.56 2.56 3.00 2.56 3.00 3.00 3.19 3.00 3.19 3.19
0.19 0.19 0.19 0.19 0.25 0.25 0.25 0.28 0.31 0.38 0.38 0.44 0.44 0.41 0.50 0.44 0.56 0.50 0.63 0.56 0.69 0.63 0.75 0.69 0.81 1.00 0.88 1.06 1.00 1.13 1.06 1.13 1.13 1.25 1.13
0.141 0.141 0.141 0.141 0.168 0.194 0.168 0.220 0.255 0.318 0.318 0.381 0.367 0.323 0.429 0.367 0.480 0.429 0.542 0.480 0.590 0.542 0.697 0.652 0.800 1.021 0.896 1.108 1.021 1.233 1.108 1.305 1.233 1.430 1.305
0.110 0.110 0.110 0.110 0.131 0.152 0.131 0.165 0.191 0.238 0.238 0.286 0.275 0.242 0.322 0.275 0.360 0.322 0.406 0.360 0.442 0.406 0.523 0.489 0.600 0.766 0.672 0.831 0.766 0.925 0.831 0.979 0.925 1.072 0.979
No. 3 No. 4 No. 5 No. 6 No. 8 No. 10 No. 8 No. 12
… 40
8
10 12 1 ⁄ 4
1 ⁄ 4
5 ⁄ 16 5 ⁄ 16
3 ⁄ 8 1 ⁄ 2
5 ⁄ 16
3 ⁄ 8
… 24
7 ⁄ 16 9 ⁄ 16
14
…
7 ⁄ 16
… 20
1 ⁄ 2 5 ⁄ 8
13
…
1 ⁄ 2
… 20
9 ⁄ 16
12
…
11 ⁄ 16
9 ⁄ 16
… 18
5 ⁄ 8 3 ⁄ 4
11
…
5 ⁄ 8
… 18
11 ⁄ 16
10
…
7 ⁄ 8
3 ⁄ 4
… 16
13 ⁄ 16
1
9 8
14 …
7 ⁄ 8
1 1 ⁄ 4 1 1 ⁄ 8 1 3 ⁄ 8 1 1 ⁄ 4 1 1 ⁄ 2 1 3 ⁄ 8 1 5 ⁄ 8 1 1 ⁄ 2 1 3 ⁄ 4
1
…
12, 14 NS
7
…
1 1 ⁄ 8
… 12
7
…
1 1 ⁄ 4
… 12
6
…
1 3 ⁄ 8
… 12
6
…
1 1 ⁄ 2
… 12 1 5 ⁄ 8 These threads are larger than nominal size to the extent that the internal thread they produce will accommodate a helical coil screw insert, which at final assembly will accept a screw thread of the nominal size and pitch. For optional necks, refer to Table 6 using dimensions for equivalent blank sizes. Ground Thread Taps: STI sizes 5 ⁄ 16 inch and smaller have external center on thread end (may be removed on bottom taps); sizes 10 through 5 ⁄ 16 inch will have an external partial cone center on shank end, with the length of the cone center approximately 1 ⁄ 4 of the diameter of shank; sizes larger than 5 ⁄ 16 inch may have internal centers on both the thread and shank ends. For runout tolerances of tap elements, refer to Table 14 using dimensions for equivalent blank sizes. For number of flutes, refer to Table 11 using dimensions for equivalent blank sizes. For general dimension tolerances, refer to Table 5b using Table 5a equivalent blank size.
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