Nut Factor (K Factor)
When working with fasteners of different frictional characteristics, the Nut, or K, Factor is used in place of a calculated coefficient of friction. The Nut Factor is an experimentally determined, dimensionless coefficient that approximates the friction of various materials and platings when applied to threaded joints. Nut Factors are generalized averages that may vary greatly given all of the variables in any bolted joint, but are useful in approximating theoretical torque values.
(L) - length of thread engagement is the length of which the female threads contact the male threads
(D) – bolt nominal diameter (inches, millimeters)
Proof Load Stress (0.2% yield)