Bottoming or shouldering of studs should be avoided by driving them only to a predetermined depth. Bottoming or shouldering causes uneven stand-out and sets up undesirable radial compressive stresses which often become relieved during service operation, permitting the stud to loosen. Tapped holes in ferrous metals should be lubricated before driving studs.
Driving torque increases directly with length of engagement. For thin-wall applications, it may be desirable to use longer engagement rather than large-pitch-diameter interference to obtain desired driving torque.
For driving into ferrous material 160 Bhn and harder, the minimum length of engagement should be 1.25D (stud diameter); the maximum and minimum major diameter limits are reduced to permit plastic flow and to reduce and stabilize driving torque.
For driving into brass and ferrous materials with a hardness less than 160 Bhn, the minimum length of engagement should also be 1.25D. For driving into other nonferrous materials, it should be 2.5D.
For lengths of engagement of 1.25D, the external thread length should be 1.5D, with a tolerance of plus 2 pitches, minus zero. For lengths of engagement of 2.5D, the length of external thread and depth of full-form thread in the tapped hole should be set at 2.75D, with a tolerance of plus 2 pitches, minus zero.