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Old 11-17-2015, 08:33 AM
David Paule David Paule is offline
 
Join Date: Dec 2009
Location: Boulder, CO
Posts: 4,875
Default Don't Change the Torque

There's no change to the assembly torque if you go with a higher-strength bolt, provided -

The thread form hasn't changed,
The material remains steel,
the head type is the same,
the thread engagement is the same,
the same washers or nuts are used,
and the same lubrication or lack of it is used upon assembly.

If all these are true, then the torque to preload relationship is unchanged, and you should use the original assembly torque to obtain the bolt preload, the clamping force, which the designers wanted. A higher-strength bolt DOES NOT need higher torque in this type of a replacement situation. It might well be damaging.

You'd use a higher torque in a wholly new design that fully uses the higher strength of the new bolt, but not for a replacement bolt.

Dave

Last edited by David Paule : 11-17-2015 at 08:37 AM.
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