Formula and input notes
Installation torque = nut factor K × nominal bolt diameter D × target clamp load F
| Input | Practical note |
|---|---|
| Clamp load | This is the target preload used by the T = KDF estimate, not the external service load on the joint. |
| Nut factor | The nut factor represents thread and bearing friction in the simplified torque-preload relationship. Use a value supported by the fastener procedure and surface condition. |
Worked bolt torque example
Bolt Torque Calculator example: KDF = 0.2 × 1 in × 5,000 lb = 1,000 in-lb, or 83.33 ft-lb. The nut factor is an assumption, not a measured joint property.
Interpret the nut-factor torque result
Use the result only when the fastener or engineering specification explicitly permits a nut-factor method with the entered K and target preload.
Friction and joint details outside T = KDF
Lubrication, coating, thread pitch and condition, prevailing torque, bearing surface, reuse, tightening method, scatter, and joint stiffness strongly affect preload.
Questions specific to this calculation
Why is the nut factor critical to the torque estimate?
The K factor represents thread and bearing-surface friction in the simplified T = KDF relationship. Lubrication, coatings, surface condition, reuse, and tightening method can change the torque needed for the same clamp load.
Can this torque result replace a manufacturer's tightening procedure?
No. Use the fastener, anchor, gasket, or equipment manufacturer's specified method and limits. Critical joints may require a controlled preload procedure rather than a generic nut-factor estimate.