Machinery's Handbook, 31st Edition
Taps 975 Table 3. Tap Thread Limits and Tolerances ANSI/ASME B94.9-2008 (R2018) Formulas for Unified Inch Screw Threads (Cut Thread) Min. Major Diameter Basic Diameter B C Min. Pitch Diameter Basic Diameter B Max. Major Diameter Min. Maj. Dia. A Max.Pitch Diameter Min. Pitch Dia. D = + + = + = + = + A = Major diameter tolerance B = Amount over basic for minimum pitch diameter C = A constant to add for major diameter: 20% of theoretical truncation for 2 to 5.5 threads per inch and 25% for 6 to 80 threads per inch D = Pitch diameter tolerance Diameter of Tap (Inch) A B D 36 or more TPI 34 or less TPI Coarser than N.F. N.F. and Finer a 0 to 0.099 0.0015 0.0002 0.0005 0.0010 0.0010 0.10 to 0.249 0.0020 0.0002 0.0005 0.0015 0.0015 1 ⁄ 4 to 3 ⁄ 8 0.0025 0.0005 0.0005 0.0020 0.0015 3 ⁄ 8 to 5 ⁄ 8 0.0030 0.0005 0.0005 0.0025 0.0020 5 ⁄ 8 to 3 ⁄ 4 0.0040 0.0005 0.0005 0.0030 0.0025 3 ⁄ 4 to 1 0.0040 0.0010 0.0010 0.0030 0.0025 1 to 1 1 ⁄ 2 0.0045 0.0010 0.0010 0.0035 0.0030 1 1 ⁄ 2 to 2 0.0055 0.0015 0.0015 0.0040 0.0030 2 to 2 1 ⁄ 4 0.0060 0.0015 0.0015 0.0045 0.0035 2 1 ⁄ 4 to 2 1 ⁄ 2 0.0060 0.0020 0.0020 0.0045 0.0035 2 1 ⁄ 2 to 3 0.0070 0.0020 0.0020 0.0050 0.0035 over 3 0.0070 0.0025 0.0025 0.0055 0.0045 a Taps over 1 1 ⁄ 2 inches with 10 or more threads per inch have tolerances for N.F. and finer.
Threads per Inch
Threads per Inch
Threads per Inch
Threads per Inch
C
C
C
C
2
0.0217 0.0173 0.0144 0.0124 0.0108 0.0096 0.0087 0.0079 0.0078
7 8 9
0.0077 0.0068 0.0060 0.0054 0.0049 0.0045 0.0042 0.0039 0.0034
18 20 22 24 26 27 28 30 32
0.0030 0.0027 0.0025 0.0023 0.0021 0.0020 0.0019 0.0018 0.0017
36 40 48 50 56 60 64 72 80
0.0015 0.0014 0.0011 0.0011 0.0010 0.0009 0.0008 0.0008 0.0007
2 1 ⁄
2
3
10 11 12 13 14 16
3 1 ⁄
2
4
4 1 ⁄
2
5
5 1 ⁄
2
6
Angle Tolerance
Deviation in Half angle
Deviation in Half angle
Threads per Inch
Deviation in Half angle
Deviation in Half angle
Threads per Inch 4 and coarser
10 to 28
± 45 ′ ± 53 ′ ± 60 ′
± 68 ′ ± 90 ′
± 30 ′ ± 35 ′ ± 40 ′
± 45 ′ ± 60 ′
30 and finer
4 1 ⁄
2 to 5 6 to 9
1 ⁄
2
Dimensions are given in inches. The tables and formulas are used in determining the limits and tolerances for cut thread metric taps having special diameter, special pitch, or both. For intermediate pitches, use value of next coarser pitch. Lead Tolerance: ± 0.003 inch within any two threads not farther apart than 1 inch. Taps over 1 1 ⁄ 2 in. with 10 or more threads per inch have tolerances for N.F. and finer.
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