How to Calculate a Bolt's Clamping Force

by Thomas Bourdin
rusty bolt image by Thor Jorgen Udvang from

The clamping force on a bolt is defined as the compressive force a fastener exerts on a joint. This is can be dependent on a number of factors, but is largely a function of the preload force, the force exerted in compressing the bolt, and the tension force, the force exerted in pulling the bolt apart. Calculating a bolt's clamping force can be accomplished with knowledge of both of these variables.

Step 1

Determine the preload force on the bolt. This force is caused by rotating the bolt, which stores force, much like a spring. This can be experimentally determined using a force transducer (if the value is not already known). As an example, assume the preload force is 2 lbs.

Step 2

Determine the tension force on the bolt. This can also be measured using a force transducer (again, if the value is not already known). Assume the tension force is 3 lbs.

Subtract the preload force from the tension force. In our example, the tension force (2 lbs.) subtracted from the preload force (3 lbs.) gives 1 lbs. This is the bolt's clamping force.

Items you will need

  • Pen or pencil
  • Paper
  • Calculator
  • Force transducer (if force values are not already known)

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