Calculating bolt torque, the force required to turn a bolt such that it delivers a known amount of tension, can be accomplished using a simple equation. This equation assumes the most rudimentary of cases; it does not account for any lubrication used on the bolt or nut, any locking mechanisms used or non-standard threads used. It is critical to apply the correct amount of torque to a bolt; under-torquing can lead to uneven loads delivered to the rest of the assembly, while over-torquing can result in failure at the secured area.
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Things you need
- Desired axial tension
Measure the diameter of the bolt using your ruler. This measurement includes the outside edge of the threads.
Find your desired bolt load in kg (or pounds). This number is dependent on the material of the bolt and thread design. It is most commonly a given value and is considered the "clamping force," according to EngineersEdge.
Multiply the diameter by the axial load, then multiply that product by 0.2. This calculation will give you the bolt torque.
Tips and warnings
- If your diameter was measured in inches, divide the bolt force by 12 to convert it to foot-lbs.
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