Sources and scope for this page: Industry convention — no single governing standard (conventional usage, definitions vary between sources), covering the definition of torque vs tension. No independent source check is recorded for this page: the content rests on the sources listed and on the working shown on the page. How sources, methods and updates are recorded.
Definition
The relationship is roughly T = K · D · F, where K is a nut factor between 0.1 and 0.3 depending on lubrication and plating, D the nominal diameter and F the desired tension. Because K varies so widely, torque is a poor proxy for tension — the same torque can produce twice the clamp load on a lubricated bolt as on a dry one.
This is why critical joints specify tension (measured by bolt stretch or an ultrasonic gauge) rather than torque, and why a torque table is only valid for the exact conditions it was compiled for.
Common misuse
Using a torque table compiled for dry, plain fasteners on lubricated or plated ones. The clamp load can be double or half what was intended.