Home / Academy / Bolt Torque Field Guide
Fasteners

Bolt Torque Field Guide

A practical guide to bolt torque, preload, friction and lubrication, with checks to make before relying on a calculated tightening value.

Torque is a means, not the target

The engineering objective is normally clamp force. Tightening torque is an indirect way of creating that preload, and a large share of the applied torque is consumed by thread and bearing-surface friction.

That is why two apparently identical bolts can develop different preload at the same wrench setting.

Lubrication changes the relationship

Lubrication, coatings, surface finish and reused threads can change friction substantially. A torque value intended for a dry fastener should not automatically be used on a lubricated assembly.

A sensible workflow

Identify the fastener specification and joint requirement first. Use a calculator for an estimate, then compare it with manufacturer data or the governing procedure. For critical joints, use the specified tightening method and inspection process.

Engineering guidance only. For safety-critical work, follow the applicable manufacturer data, drawings, standards and competent professional judgement.