Enter the torque, nominal diameter, and axial force into the calculator to determine the Bolt Friction Coefficient.

Bolt Friction Coefficient Formula

The following formula is used to calculate the Bolt Friction Coefficient. 

CoF = T / (d * F)

Variables:

  • CoF is the Bolt Friction Coefficient (no units)
  • T is the torque required to tighten the bolt (Nm)
  • d is the nominal diameter of the bolt (m)
  • F is the axial force applied on the bolt (N)

To calculate the Bolt Friction Coefficient, divide the torque required to tighten the bolt by the product of the nominal diameter of the bolt and the axial force applied on the bolt. This will give the coefficient of friction between the threads of the bolt and the material it is being fastened into.

What is a Bolt Friction Coefficient?

The Bolt Friction Coefficient, also known as the coefficient of friction (CoF), is a value that represents the amount of friction between two surfaces – in this case, the threads of a bolt and the material it is being fastened into. This value is crucial in determining the torque required to tighten a bolt without causing damage or failure. It is influenced by factors such as the materials of the surfaces, the presence of lubrication, and the roughness of the surfaces.

How to Calculate Bolt Friction Coefficient?

The following steps outline how to calculate the Bolt Friction Coefficient (CoF).

  1. First, determine the torque required to tighten the bolt (T) in Newton-meters (Nm).
  2. Next, determine the nominal diameter of the bolt (d) in meters (m).
  3. Next, determine the axial force applied on the bolt (F) in Newtons (N).
  4. Next, gather the formula from above: CoF = T / (d * F).
  5. Finally, calculate the Bolt Friction Coefficient (CoF) using the formula.
  6. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem:

Use the following variables as an example problem to test your knowledge.

Torque required to tighten the bolt (T) = 50 Nm

Nominal diameter of the bolt (d) = 0.02 m

Axial force applied on the bolt (F) = 1000 N