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Bolt Torque, Clamp Force & Effective Nut Factor

Explore torque and clamp force using a selected nut factor, nominal diameter and an explicit percentage adjustment.

  • Formula & worked example
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Calculator inputs

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How to use this calculator

  1. Enter the known values in the units shown. Results update as you type.
  2. Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
  3. Use the worked example to check the method. Reset restores the starting fields.

Private by default

Inputs and results stay in this browser tab. Bookify does not upload or store the values you enter.

Formula and method

A nut factor of 0.20, a 10 mm nominal diameter and a target clamp force of 10,000 N give 20 N·m with no further adjustment. A 40 percent adjustment gives 12 N·m.

Torque = K × clamp force × nominal diameter × (1 − adjustment/100)

Worked example

Enter these known values and leave the other values blank.

Nominal bolt diameter
10 mm
Target or inferred clamp force
10000 N
Base nut factor K
0.2
Additional torque reduction
0 %
Modeled tightening torque
20 N·m

Assumptions and limitations

  • K is an empirical nut factor for the bolt, coating, thread and bearing conditions. The effective factor used here is K times one minus the additional reduction fraction.
  • The presets are illustrative captured coefficients, not qualified torque specifications. If K already accounts for the actual lubricant, select no additional reduction to avoid counting lubrication twice.
  • Diameter, clamp force, torque and K are positive. Additional reduction ranges from zero up to, but excluding, 100 percent.
  • The calculation does not check bolt grade, proof load, yielding, thread engagement, fatigue, joint stiffness or tightening scatter. Use the assembly manufacturer’s validated specification for installation.

Common questions

Should I add another lubrication reduction to an already lubricated K?

Usually that would count the same effect twice. Use a factor calibrated to the assembly and no additional reduction unless that separate adjustment is justified.

Does this set a safe torque for any bolt?

No. It evaluates a torque/preload model. The assembly’s allowable load and installation torque need separate verification.

References

Bookify excludes a 100 percent torque-reduction factor because it makes positive clamp force unrecoverable from the torque model. The pound-force uses the exact international pound and standard gravity instead of the rounded captured factor. Kilogram-force centimeters use standard gravity and exactly one centimeter. Pound-force feet use the exact international pound and foot with standard gravity. Pound-force inches use the exact international pound and inch with standard gravity.

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