Metric Thread Limits For Standard and Special and Metric Threads
Ground Thread Tap Limits (USCTI Table 341)
The following tables and formula are used in determining the limits and tolerances for ground thread metric taps unless otherwise specified. They apply only to metric threads having a 60° form with a P/8 flat at the major diameter of the basic thread form.
LEAD TOLERANCE A maximum lead deviation of ±0.013 mm within any two threads not farther apart than 25 mm is permitted. ANGLE TOLERANCE Pitch (mm) Deviation in Half Angle Over 0.25 to 2.5 incl. ± 30’ Over 2.5 to 4. incl. ± 25’ Over 4 to 6 incl. ± 20’ FORMULA Min. Major Dia = Basic + W Max. Pitch Dia. = Basic + Y Max. Major Dia. = Min. + X Min. Pitch Dia. = Max. - Z
W = Constant to add to Basic Major Diameter* X = Major Diameter Tolerance Y = Amount over Basic for Maximum Pitch Diameter Z = Pitch Diameter Tolerance
*W = .080P Converted to inches
Note: When 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 Y, plus the basic single height of thread, plus constant W.
Tap Limits for Metric Threads (inch)
Symetrical Thread Height
Y
Z
Pitch
Over M6.3 to M25 Incl.
Over M25 To M90 Incl.
Over M6.3 to M25 Incl.
Over M25 To M90 Incl.
W X
M1.6 To M6.3 Incl.
M1.6 To M6.3 Incl.
Over M90
Over M90
0.64952P (Inch)
mm Inch Equiv.
0.3 0.011811 0.007671 0.0009 0.0010 0.0015 0.0015 0.0020 0.0020 0.0006 0.0006 0.0008 0.0008 0.35 0.013779 0.008950 0.0011 0.0010 0.0015 0.0015 0.0020 0.0020 0.0006 0.0006 0.0008 0.0008 0.4 0.015748 0.010229 0.0013 0.0010 0.0015 0.0020 0.0020 0.0020 0.0006 0.0006 0.0008 0.0010 0.45 0.017716 0.011507 0.0014 0.0010 0.0015 0.0020 0.0020 0.0020 0.0006 0.0008 0.0008 0.0010 0.5 0.019685 0.012786 0.0016 0.0010 0.0015 0.0020 0.0020 0.0025 0.0006 0.0008 0.0010 0.0010 0.6 0.236220 0.015343 0.0019 0.0010 0.0020 0.0020 0.0025 0.0025 0.0008 0.0008 0.0010 0.0010 0.7 0.027559 0.017900 0.0022 0.0016 0.0020 0.0020 0.0025 0.0025 0.0008 0.0008 0.0010 0.0010 0.75 0.029527 0.019178 0.0024 0.0016 0.0020 0.0025 0.0025 0.0030 0.0008 0.0010 0.0010 0.0012 0.8 0.031496 0.020457 0.0025 0.0016 0.0020 0.0025 0.0025 0.0030 0.0008 0.0010 0.0010 0.0012 0.9 0.035433 0.023014 0.0028 0.0016 0.0020 0.0025 0.0025 0.0030 0.0008 0.0010 0.0010 0.0012 1.0 0.039370 0.025572 0.0032 0.0016 0.0025 0.0025 0.0030 0.0030 0.0010 0.0010 0.0012 0.0012 1.25 0.049212 0.031964 0.0039 0.0025 0.0025 0.0025 0.0030 0.0035 0.0010 0.0012 0.0012 0.0016 1.5 0.059055 0.038357 0.0047 0.0025 0.0025 0.0030 0.0030 0.0035 0.0010 0.0012 0.0012 0.0016 1.75 0.068897 0.044750 0.0055 0.0025 – 0.0030 0.0035 0.0040 – 0.0012 0.0016 0.0016 2.0 0.078740 0.051143 0.0063 0.0025 – 0.0035 0.0035 0.0040 – 0.0016 0.0016 0.0016 2.5 0.098425 0.063929 0.0079 0.0025 – 0.0035 0.0040 0.0045 – 0.0016 0.0016 0.0020 3.0 0.118110 0.076715 0.0095 0.0039 – 0.0040 0.0040 0.0050 – 0.0016 0.0020 0.0020 3.5 0.137795 0.089501 0.0110 0.0039 – 0.0040 0.0045 0.0050 – 0.0016 0.0020 0.0020 4.0 0.157480 0.102286 0.0126 0.0039 – 0.0040 0.0045 0.0055 – 0.0020 0.0020 0.0025 4.5 0.177165 0.115072 0.0142 0.0039 – – 0.0050 0.0055 – 0.0020 0.0020 0.0025 5.0 0.196850 0.127858 0.0158 0.0039 – – 0.0050 0.0060 – – 0.0025 0.0025 5.5 0.216535 0.140644 0.0173 0.0039 – – 0.0055 0.0060 – – 0.0025 0.0025 6.0 0.236220 0.153430 0.0189 0.0039 – – 0.0055 0.0060 – – 0.0025 0.0025 For intermediate pitches use value for next coarser pitch. Symmetrical Thread Height; Equivalent to the basic height, h, of the original American National Form.
Threading Technical
773
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