American Bolt Corporation

Torque Tightening Guide

It has been reported that approximately 50% of applied torque is needed to overcome the friction caused by the nut/bolt bearing surface being applied against the mating joint surface. Approximately 40% of the applied torque is needed to overcome the friction of the mating thread surfaces. Only approximately 10% of the applied torque produces tension in the bolt.

Many variables can affect the torque tension relationship. The following are some known examples of factors that can influence the actual pre-load achieved by a given application torque:

Joint design
The hardness and type of materials of the mating joint members
Natural variation of joint/fastener dimensions due to manufacturing processes
Surface finish of the parts
Percentage of thread flank engagement
Hole clearance
Perpendicularity of the contact surfaces
Supplemental coatings, thickness and lubricity
High performance additional lubricants
Cut vs. rolled threads
Interference caused by burrs, thread nicks, dirt etc.
Type and accuracy of tool used to tighten the fastener
The speed of tightening
Where torque is applied (head of bolt vs. nut)
Operator influence
Job conditions

Any values supplied by American Bolt Corp. are intended to provide only a target torque. The only accurate way to establish a specific pre-load is through torque tension testing of the fasteners to be used in the actual joint.

Torque Charts