Torque 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. Therefore, 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