DERIVATION OF EQUATION USED IN DETERMINING LENGTH OF
ENGAGEMENT OF THREADS
Shear force of male=Force on female
A1 = cylindrical shear area at assumed diameter
d =minimum minor diameter of screw
R =maximum major radius of nut
SS = shear stress
L = length of engagement
P = pressure
Applying a safety factor of 1.5 yields
Figure 104. Thread parameters.
†L/2 is substituted for L since only one-half (approximately) of the thread length actually is loaded in shear while resisting
the internal pressure.