How this calculator works
The nut factor compresses thread geometry and friction effects into one empirical coefficient. Surface treatment and lubrication are already part of K. Torque control can produce substantial preload scatter; use the fastener or equipment specification and account for proof load and joint behaviour.
Formula
T = K F d; F = T/(Kd); d = T/(KF); K = T/(Fd). SI uses N m, N and m.
Worked example
With K = 0.2, a 10 mm bolt and 10 kN target preload, T = 0.2 x 10000 x 0.01 = 20 N m.
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Frequently asked questions
Is 0.2 correct for every dry bolt?
No. It is an illustrative default. Obtain the effective coefficient for the specific bolt, nut, finish and assembly process.
Should I multiply by a lubricant factor too?
No. Use a K value for the lubricated condition. Applying another reduction can double-count friction changes.
Does this check bolt strength?
No. Proof load, yield, thread stripping, fatigue and joint separation require separate checks.