Machinery's Handbook, 31st Edition
2110
Interference-Fit Threads Table 4. Allowances for Coarse Thread Series ANSI/ASME B1.12-1987 (R2018)
Difference between Nom. Size and Max Major Diam. of NC-5 CSF or NC-5 ONF a
Difference between Basic Minor Diam. and Min Minor
Difference between Basic Minor Diam. and Min Minor Diam.of NC-5 INF
Difference between Max Minor Diam. and Basic Minor Diam., Ext Thread
Difference between Nom. Size and Max Major Diam of NC-5 HF a
Max PD Inteference or Neg Allowance, Ext Thread b
Diam. of NC-5 IF a
TPI
20 18 16 14 13 12 11 10
0.0030 0.0045 0.0060 0.0070 0.0080 0.0085 0.0110 0.0140 0.0150 0.0165 0.0180 0.0190
0.0030 0.0035 0.0040 0.0045 0.0050 0.0050 0.0055 0.0060 0.0065 0.0065 0.0070 0.0070
0.000 0.000 0.000 0.014 0.014 0.016 0.017 0.019 0.022 0.025 0.030 0.034
0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000
0.0055 0.0065 0.0070 0.0080 0.0084 0.0092 0.0098 0.0105 0.0116 0.0128 0.0143 0.0172
0.0072 0.0080 0.0090 0.0103 0.0111 0.0120 0.0131 0.0144 0.0160 0.0180 0.0206 0.0241
9 8 7 6
a The allowances in these columns were obtained from industrial research data. b Negative allowance is the difference between the basic pitch diameter and pitch diameter value at maximum material condition. All dimensions are in inches. The difference between basic major diameter and internal thread minimum major diameter is 0.075 H and is tabulated in Table 5. Table 5. Tolerances for Pitch Diameter, Major Diameter, and Minor Diameter for Coarse Thread Series ANSI/ASME B1.12-1987 (R2018)
Minor Diam. Tolerance for Int Thread NC-5 INF c
Minor Diam. Tolerance for Int Thread NC-5 IF
Tolerance 0.075 H or 0.065 P for Tap Major Diam.
PD Tolerance for Ext and Int Threads a
Major Diam. Tolerance for Ext Thread b
TPI
20 18 16 14 13 12 11 10
0.0026 0.0030 0.0032 0.0036 0.0037 0.0040 0.0042 0.0045 0.0049 0.0054 0.0059 0.0071
0.0052 0.0060 0.0064 0.0072 0.0074 0.0080 0.0084 0.0090 0.0098 0.0108 0.0118 0.0142
0.010 0.011 0.011 0.008 0.008 0.009 0.010 0.011 0.012 0.014 0.015 0.018
0.010 0.011 0.011 0.012 0.012 0.013 0.013 0.014 0.014 0.015 0.015 0.018
0.0032 0.0036 0.0041 0.0046 0.0050 0.0054 0.0059 0.0065 0.0072 0.0093 0.0093 0.0108
9 8 7 6
a National Class 3 pitch diameter tolerance from ASA B1.1-1960. b Twice the NC-3 pitch diameter tolerance. c National Class 3 minor diameter tolerance from ASA B1.1-1960. All dimensions are in inches.
Relation of Driving Torque to Length of Engagement: Torques increase directly as the length of engagement and this increase is proportionately more rapid as size increases. The standard does not establish recommended breakloose torques. Surface Roughness: Surface roughnesss is not a required measurement. Roughness between 63 and 125 μ in Ra is recommended. Surface roughness greater than 125 μ in Ra may encourage galling and tearing of threads. Surfaces with roughness less than 63 μ in Ra may hold insufficient lubricant and wring or weld together.
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