The practical idea
Bolt preload is the tension created in a fastener when it is tightened. That tension clamps the joint together. The tightening torque is only a convenient input; most of it is consumed by friction under the head and in the threads.
What changes the real result?
The same torque can create very different preload when lubrication, coatings, surface finish or reused fasteners change friction. For critical joints, use the specified tightening procedure and validated data rather than a generic K factor.
A reliable workflow
- Confirm the units, material and operating conditions.
- Use a suitable formula or reference as a starting point.
- Compare the estimate with manufacturer data and applicable standards.
- Measure the real result and record any corrections for repeat work.
Apply the guide