Bolt Torque
Estimate the required tightening torque to achieve proper clamping force for standard industrial fasteners.
The K-Factor Trap
Torque is a terrible way to measure clamp force, but it is the only practical method we have in the field. When you pull on a torque wrench, up to 90% of your effort goes into overcoming friction under the bolt head and in the threads. Only 10% actually stretches the bolt to create clamping force.
This is why the K-Factor (friction coefficient) is critical. If you calculate torque for a dry, rusty bolt (K=0.30) but a mechanic applies anti-seize (K=0.12) and uses that same torque spec, they will drastically over-stretch and likely snap the bolt.
Best Practices
- Never apply lubrication or anti-seize to a bolt unless the engineering specification explicitly calls for it.
- If you must use anti-seize on a bolt originally specified for dry assembly, reduce the applied torque by approximately 40%.