Thread Limits, Tolerances & Formulas
Ground Thread Taps (USCTI Table 331) The following tables and formula are used in determining the limits and tolerances for ground thread taps having a thread lead angle not in excess of 5-degrees, inless otherwise specified.
LEAD TOLERANCE A maximum lead deviation of ± 0.0005”, within any two threads not farther apart than 1” is permitted. ANGLE TOLERANCE Threads Per Inch Deviation in Half Angle 4 to 5-1/2 incl. ± 20’ 6 to 9 incl. ± 25’ 10 to 80 incl. ± 30’ FORMULA Max. Major Dia. = Basic + A Max. Pitch Dia. = Min. + D Min. Major Dia. = Basic + B Min. Pitch Dia. = Basic + C In the above formula: A = Constant to add = 0.130P for all Pitches B = Major Diameter Tolerance = 0.087P for 48 Through 80 TPI
= 0.076P for 36 Through 47 TPI = 0.065P for 4 Through 35 TPI
C = Amount over basic for minimum pitch diameter D = Pitch diameter tolerance
Note: W hen the tap major diameter must be determined from a specified tap pitch diameter, the maximum major diameter equals the minimum specified pitch diameter minus Constant C, plus 0.64952P, plus Constant A.
C
D
Threads Per Inch
A
B
Over 5/8” to 2-1/2 Incl.
Over 2-1/2” 0.0015 0.0015 0.0015 0.0015 0.0015 0.0015 0.0015 0.0015 0.0015 0.0015 0.0015 0.0015 0.0015 0.0015 0.0015 0.0015 0.0015 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020
To 1” Incl.
Over 1” to 1-1/2” Incl.
Over 1-1/2” to 2-1/2” Incl.
To 5/8” Incl.
Over 2-1/2”
80 72 64 56 48 44 40 36 32 28 24 20 18 16 14 13 12 11 10
0.0016 0.0018 0.0020 0.0023 0.0027 0.0030 0.0032 0.0036 0.0041 0.0046 0.0054 0.0065 0.0072 0.0081 0.0093 0.0100 0.0108 0.0118 0.0130 0.0144 0.0162 0.0186 0.0217 0.0236 0.0260 0.0289 0.0325
0.0011 0.0012 0.0014 0.0016 0.0018 0.0017 0.0019 0.0021 0.0020 0.0023 0.0027 0.0032 0.0036 0.0041 0.0046 0.0050 0.0054 0.0059 0.0065 0.0072 0.0081 0.0093 0.0108 0.0118 0.0130 0.0144 0.0162
0.0005 0.0005 0.0005 0.0005 0.0005 0.0005 0.0005 0.0005 0.0010 0.0010 0.0010 0.0010 0.0010 0.0010 0.0010 0.0010 0.0010 0.0010
0.0010 0.0010 0.0010 0.0010 0.0010 0.0010 0.0010 0.0010 0.0010 0.0010 0.0010 0.0010 0.0010 0.0010 0.0015 0.0015 0.0015 0.0015 0.0015 0.0015 0.0015 0.0015 0.0015 0.0015 0.0015 0.0015 0.0015
0.0005 0.0005 0.0005 0.0005 0.0005 0.0005 0.0005 0.0005 0.0005 0.0005 0.0005 0.0005 0.0005 0.0005 0.0005 0.0005 0.0005 0.0005 0.0005 0.0005 0.0005 0.0010 0.0010 0.0010 0.0010 0.0010 0.0010
0.0010 0.0010 0.0010 0.0010 0.0010 0.0010 0.0010 0.0010 0.0010 0.0010 0.0010 0.0010 0.0010 0.0010 0.0010 0.0010 0.0010 0.0010 0.0010 0.0010 0.0010 0.0010 0.0010 0.0015 0.0015 0.0015 0.0015
0.0010 0.0010 0.0010 0.0010 0.0010 0.0010 0.0010 0.0010 0.0010 0.0010 0.0015 0.0015 0.0015 0.0015 0.0015 0.0015 0.0015 0.0015 0.0015 0.0015 0.0015 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020
0.0015 0.0015 0.0015 0.0015 0.0015 0.0015 0.0015 0.0015 0.0015 0.0015 0.0015 0.0015 0.0015 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0025 0.0025 0.0025 0.0025 0.0025 0.0025
– – – – – – – – –
9 8 7 6
5 1/2
5
4 1/2
4
For intermediate pitches, use values for next coarser pitch for C and D, but use formulas for A and B.
Threading Technical
771
osgtool.com
Powered by FlippingBook