Torque mostly fights friction

Roughly 90% of tightening torque is lost to friction; only ~10% actually stretches the bolt.

Why it works

About half goes to under-head friction, ~40% to thread friction. That is why lubrication changes preload so dramatically at the same torque.

Do it exactly

Estimate with the rule, then check it against the calculator that models it properly.

Open Bolt Torque & Preload →

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