Threads & fasteners
Bolt Preload vs Tightening Torque
Understand why tightening torque is only an indirect way to create bolt preload and why friction dominates many torque estimates.
Use the calculation tool
Open Thread & Bolt Calculator →Preload is the engineering target
In a preloaded bolted joint, the important quantity is usually clamp force. Tightening torque is a practical installation input used to create that preload.
Why torque is uncertain
A large part of tightening torque is consumed by friction in the threads and under the bearing surface. Changes in lubrication, coating, surface finish and washer geometry can therefore change preload significantly even when the same torque is applied.
What DraftFit estimates
The DraftFit bolt tool uses an engineering torque model with explicit friction inputs. Treat the result as an estimate unless the joint has a validated tightening procedure and friction data.
Related standards
DraftFit guides are engineering educational content and do not replace the controlled standard, project specification or responsible-engineer review.