Machinery's Handbook, 31st Edition
1004
Taps Table 23c. ASME Standard Straight Pipe Thread Limits: NPSF Ground Thread Dryseal ANSI Standard Straight Pipe Thread Form (NPSF) ANSI/ASME B94.9-2008 (R2018) Formulas For American Dryseal (NPSF) Ground Thread Taps Nominal Size, Inches Major Diameter Pitch Diameter Max. Minor Dia. Min. G Max. H Min. K Max. L 1 ⁄ 16 H - 0.0010 K + Q - 0.0005 L - 0.0005 E - F M - Q 1 ⁄ 8 H - 0.0010 K + Q - 0.0005 L - 0.0005 E - F M - Q 1 ⁄ 4 H - 0.0010 K + Q - 0.0005 L - 0.0005 E - F M - Q 3 ⁄ 8 H - 0.0010 K + Q - 0.0005 L - 0.0005 E - F M - Q 1 ⁄ 2 H - 0.0010 K + Q - 0.0005 L - 0.0005 E - F M - Q 3 ⁄ 4 H - 0.0010 K + Q - 0.0005 L - 0.0005 E - F M - Q Values to Use in Formulas Threads per Inch E F M Q 27 Pitch diameter of plug at gaging notch 0.0035 Actual measured pitch diameter 0.0251 18 0.0052 0.0395 14 0.0067 0.0533 All dimensions are given in inches. Lead Tolerance: A maximum lead deviation of ± 0.0005 inch within any two threads not farther apart than one inch. Angle Tolerance: Plus or minus 30 min. in half angle for 14 to 27 threads per inch, inclusive. Table 23d. ANSI Standard Straight Pipe Tap Limits: (NPS) Cut Thread ANSI Straight Pipe Thread Form (NPSC) ANSI/ASME B94.9-2008 (R2018)
Threads per Inch, NPS, NPSC
Values to Use in Formulas
Pitch Diameter
Size at Gaging Notch 0.3736 0.4916 0.6270 0.7784 0.9889 1.2386
Nominal Size
Min.
Max.
A
B
C
27 18 18 14 14
0.3721 0.4908 0.6257 0.7776 0.9876 1.2372
0.3751 0.4938 0.6292 0.7811 0.9916 1.2412
0.0267
0.0296
0.0257
1 ⁄ 8 1 ⁄ 4 3 ⁄ 8 1 ⁄ 2 3 ⁄ 4
0.0408
0.0444
0.0401
0.0535
0.0571
0.0525
1
0.0658
0.0696
0.0647
11 1 ⁄ 2
The following are approximate formulas, in which M = measured pitch diameter in inches: Major dia., min. = M + A Major dia., max. = M + B Minor dia., max. = M - C Maximum pitch diameter of tap is based on an allowance deducted from the maximum product pitch diameter of NPSC. Minimum pitch diameter of tap equals maximum pitch diameter minus the tolerance. All dimensions are given in inches. Lead Tolerance: ± 0.003 inch per inch of thread. Angle Tolerance: For all pitches, tolerance will be ± 45 ″ for half angle and ± 68 ″ for full angle. Taps made to these specifications are to be marked NPS and used for NPSC thread form. Taps made to the specifications in Table 23a are to be marked NPS and used for NPSC. As the American National Standard straight pipe thread form is to be maintained, the major and minor diameters vary with the pitch diameter. Either a flat or rounded form is allowable at both the crest and the root.
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