The bolt-torque shortcut

Tightening torque ≈ 0.2 × preload × bolt diameter (dry steel).

Why it works

T = K·F·d with a nut factor K ≈ 0.2 for unlubricated steel. Lubrication drops K toward 0.12–0.15 — same torque, much higher preload.

Do it exactly

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

Open Bolt Torque & Preload →

More in Mechanical

• Torque mostly fights frictionRoughly 90% of tightening torque is lost to friction; only ~10% actually stretches the bolt.
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Browse all 96 rules of thumb →