Interference-Fit Threads OTHER THREADS Interference-Fit Threads Machinery's Handbook, 31st Edition
2106
Interference-Fit Threads.— Interference-fit threads are threads in which the externally threaded member is larger than the internally threaded member when both members are in the free state and that, when assembled, become the same size and develop a holding torque through elastic compression, plastic movement of material, or both. By custom, these threads are designated Class 5. The data in Table 1, Table 2, and Table 3 , which are based on years of research, testing and field study, represent an American standard for interference-fit threads that overcomes the difficulties experienced with previous interference-fit recommendations such as are given in Federal Screw Thread Handbook H28. These data were adopted as American Standard ASA B1.12-1963. Subsequently, the standard was revised and issued as American National Standard ANSI B1.12-1972. More recent research conducted by the Portsmouth Naval Shipyard has led to the current revision ANSI/ASME B1.12-1987 (R2018). The data in Table 1, Table 2, and Table 3 provide dimensions for external and internal interference-fit (Class 5) threads of modified American National form in the Coarse Thread series, sizes 1 ∕ 4 inch to 1 1 ∕ 2 inches. It is intended that interference-fit threads conforming with this standard will provide adequate torque conditions which fall within the limits shown in Table 3 . The minimum torques are intended to be sufficient to ensure that externally threaded members will not loosen in service; the maximum torques establish a ceiling below which seizing, galling, or torsional failure of the externally threaded components is reduced. Table 1 and Table 2 give external and internal thread dimensions and are based on engagement lengths, external thread lengths, and tapping hole depths specified in Table 3 and in compliance with the design and application data given in the following paragraphs. Table 4 gives the allowances and Table 5 gives the tolerances for pitch, major, and minor diameters for the Coarse Thread Series. .125 P .125 H
Major Dia.
60˚
.625 H
H
30˚
.5 P
Pitch Dia.
.250 H
.250 P
Minor Dia.
P
90˚
Axis of Screw Thread
Basic Profile of American National Standard Class 5 Interference Fit Thread
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