Taps Table 2. Tap Thread Limits and Tolerances ANSI/ASME B94.9-2008 (R2018) Formulas for Unified Inch Screw Threads (Ground Thread) Max.Major Diameter Basic Diameter A Max.Pitch Diameter Basic Diameter C Min. Major Diameter Max. Maj. Dia. B Min.Pitch Diameter Max. Pitch Dia. D = + = + = − = − A = Constant to add = 0.130 P for all pitches B = Major diameter tolerance= 0.087 P for 48 to 80 TPI; 0.076 P for 36 to 47 TPI; 0.065 P for 4 to 35 TPI C = Amount over basic for maximum pitch diameter D = Pitch Diameter Tolerance Threads per Inch A B C D 0 to 5 ⁄ 8 5 ⁄ 8 to 1 1 to 1 1 ⁄ 2 1 1 ⁄ 2 to 2 1 ⁄ 2 Over 2 1 ⁄ 2 0 to 5 ⁄ 8 5 ⁄ 8 to 1 1 to 1 1 ⁄ 2 1 1 ⁄ 2 to 2 1 ⁄ 2 Over 2 1 ⁄ 2 80 0.0016 0.0011 0.0010 0.0015 0.0020 0.0020 0.0030 0.0005 0.0005 0.0010 0.0010 0.0015 72 0.0018 0.0012 0.0010 0.0015 0.0020 0.0020 0.0030 0.0005 0.0005 0.0010 0.0010 0.0015 64 0.0020 0.0014 0.0010 0.0015 0.0020 0.0020 0.0030 0.0005 0.0005 0.0010 0.0010 0.0015 56 0.0023 0.0016 0.0010 0.0015 0.0020 0.0020 0.0030 0.0005 0.0005 0.0010 0.0010 0.0015 48 0.0027 0.0018 0.0010 0.0015 0.0020 0.0020 0.0030 0.0005 0.0005 0.0010 0.0010 0.0015 44 0.0030 0.0017 0.0010 0.0015 0.0020 0.0020 0.0030 0.0005 0.0005 0.0010 0.0010 0.0015 40 0.0032 0.0019 0.0010 0.0015 0.0020 0.0020 0.0030 0.0005 0.0005 0.0010 0.0010 0.0015 36 0.0036 0.0021 0.0010 0.0015 0.0020 0.0020 0.0030 0.0005 0.0005 0.0010 0.0010 0.0015 32 0.0041 0.0020 0.0015 0.0015 0.0020 0.0020 0.0030 0.0005 0.0005 0.0010 0.0010 0.0015 28 0.0046 0.0023 0.0015 0.0015 0.0020 0.0020 0.0030 0.0005 0.0005 0.0010 0.0010 0.0015 24 0.0054 0.0027 0.0015 0.0015 0.0020 0.0025 0.0030 0.0005 0.0005 0.0010 0.0015 0.0015 20 0.0065 0.0032 0.0015 0.0015 0.0020 0.0025 0.0030 0.0005 0.0005 0.0010 0.0015 0.0015 18 0.0072 0.0036 0.0015 0.0015 0.0020 0.0025 0.0030 0.0005 0.0005 0.0010 0.0015 0.0015 16 0.0081 0.0041 0.0015 0.0015 0.0020 0.0025 0.0035 0.0005 0.0005 0.0010 0.0015 0.0020 14 0.0093 0.0046 0.0015 0.0020 0.0025 0.0030 0.0035 0.0005 0.0005 0.0010 0.0015 0.0020 13 0.0100 0.0050 0.0015 0.0020 0.0025 0.0030 0.0035 0.0005 0.0005 0.0010 0.0015 0.0020 12 0.0108 0.0054 0.0015 0.0020 0.0025 0.0030 0.0035 0.0005 0.0005 0.0010 0.0015 0.0020 11 0.0118 0.0059 0.0015 0.0020 0.0025 0.0030 0.0040 0.0005 0.0005 0.0010 0.0015 0.0020 10 0.0130 0.0065 … 0.0020 0.0025 0.0030 0.0040 … 0.0005 0.0010 0.0015 0.0020 9 0.0144 0.0072 … 0.0020 0.0025 0.0030 0.0040 … 0.0005 0.0010 0.0015 0.0020 8 0.0162 0.0081 … 0.0020 0.0025 0.0030 0.0040 … 0.0005 0.0010 0.0015 0.0020 7 0.0186 0.0093 … 0.0025 0.0025 0.0035 0.0045 … 0.0010 0.0010 0.0020 0.0025 6 0.0217 0.0108 … 0.0025 0.0025 0.0035 0.0045 … 0.0010 0.0010 0.0020 0.0025 5 1 ⁄ 2 0.0236 0.0118 … 0.0025 0.0030 0.0035 0.0045 … 0.0010 0.0015 0.0020 0.0025 5 0.0260 0.0130 … 0.0025 0.0030 0.0035 0.0045 … 0.0010 0.0015 0.0020 0.0025 4 1 ⁄ 2 0.0289 0.0144 … 0.0025 0.0030 0.0035 0.0045 … 0.0010 0.0015 0.0020 0.0025 4 0.0325 0.0162 … 0.0025 0.0030 0.0035 0.0045 … 0.0010 0.0015 0.0020 0.0025 Dimensions are given in inches. The tables and formulas are used in determining the limits and tolerances for ground thread taps having a thread lead angle not in excess of 5 ° , unless otherwise specified. The tap major diameter must be determined from a specified tap pitch diameter: the minimum major diameter equals the maximum specified tap pitch diameter minus constant C , plus 0.64951904 P plus constant A . Minimum Major Diameter Tap Pitch Diameter C 0.64951904 P A = − + + For intermediate pitches, use value of next coarser pitch; for C and D use formulas for A and B . Lead Tolerance: ± 0.0005 inch within any two threads not farther apart than 1 inch. Angle Tolerance: ± 20 ′ in half angle for 4 to 5 1 ⁄ 2 pitch; ± 25 ′ in half angle for 6 to 9 pitch; and ± 30 ′ in half angle for 10 to 80 pitch. Machinery's Handbook, 31st Edition
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