Machinery's Handbook, 31st Edition
Taps
1003
Table 23a. Straight Pipe Thread Limits: NPS, Ground Thread ANSI Straight Pipe Thread Form (NPSC, NPSM) ANSI/ASME B94.9-2008 (R2018)
Major Diameter
Pitch Diameter
Threads per Inch, NPS, NPSC, NPSM
Plug at Gaging Notch E
Nominal Size, Inches
Plug at Gaging Notch
Min. G
Max. H
Min. K
Max. L
27 18 18 14 14
0.3983 0.4022 0.4032 0.3736 0.3746 0.3751 0.5286 0.5347 0.5357 0.4916 0.4933 0.4938 0.6640 0.6701 0.6711 0.6270 0.6287 0.6292 0.8260 0.8347 0.8357 0.7784 0.7806 0.7811 1.0364 1.0447 1.0457 0.9889 0.9906 0.9916 1.2966 1.3062 1.3077 1.2386 1.2402 1.2412
1 ⁄ 1 ⁄ 3 ⁄ 1 ⁄ 3 ⁄
8 4 8 2
4
1
11 1 ⁄
2
Formulas for NPS Ground Thread Taps a
Minor Dia. Max. M - B M - B M - B
Threads per Inch
Major Diameter
A
B
Nominal Size
Min. G
Max. H
27 18 14
0.0296 0.0257 0.0444 0.0401 0.0571 0.0525 0.0696 0.0647
H - 0.0010 ( K + A ) - 0.0010 H - 0.0010 ( K + A ) - 0.0020 H - 0.0015 ( K + A ) - 0.0021
1 ⁄
8
4 to
1 ⁄
3 ⁄
4
1
11 1 ⁄
2
a In the formulas, M equals the actual measured pitch diameter. All dimensions are given in inches. Maximum pitch diameter of tap is based upon an allowance deducted from the maximum product pitch diameter of NPSC or NPSM, whichever is smaller. Minimum pitch diameter of tap is derived by subtracting the ground thread pitch diameter tolerance for actual equivalent size. Lead tolerance: A maximum lead deviation pf ± 0.0005 inch within any two threads not farther apart than one inch. Angle Tolerance: 11 1 ⁄ 2 to 27 threads per inch, plus or minus 30 min. in half angle. Taps made to the specifications in Table 23a are to be marked NPS and used for NPSC and NPSM. Table 23b. Straight Pipe Thread Limits: NPSF Ground Thread ANSI Standard Straight Pipe Thread Form (NPSF) ANSI/ASME B94.9-2008 (R2018)
Major Diameter
Pitch Diameter
Minor a Dia. Flat, Max.
Plug at Gaging Notch E
Nominal Size, Inches
Threads per Inch
Min. K
Max. L
Min. G
Max. H
27 27 18 18 14 14
0.3008 0.3018 0.2812 0.2772 0.2777 0.004 0.3932 0.3942 0.3736 0.3696 0.3701 0.004 0.5239 0.5249 0.4916 0.4859 0.4864 0.005 0.6593 0.6603 0.6270 0.6213 0.6218 0.005 0.8230 0.8240 0.7784 0.7712 0.7717 0.005 1.0335 1.0345 0.9889 0.9817 0.9822 0.005
1 ⁄
16
1 ⁄ 1 ⁄ 3 ⁄ 1 ⁄ 3 ⁄
8 4 8 2 4
a As specified or sharper. All dimensions are given in inches.
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