This question came up while working on a project this weekend and I'm
looking for some input.
Let's say I've got a nut and bolt holding something together and I
want it torqued at XXX inch-pounds. I can hold the nut with a standard
wrench and use the torque wrench on the bolt, or I can hold the bolt
with a standard wrench and use the torque wrench on the nut.
One of the guys I was working with said "When given the chance, you
always torque the nut." When I asked why the answer was "Because
that's what I've always been told." You know how *those* conversations
So what's the deal? Does it matter? And if so, why? Could it be
different in different cases? And if so, why?
re: It does not matter. The braking effect of the underside of the
nut is equivalent to the braking effect of the underside of the bolt
Even if the material on the underside of the nut is not equivalent to
the material on the underside of the bolt head?
In such a case the difference would still likely be minimal. It's not
like you're going to use an aluminum nut with steel bolt.
Torque specs vary on bolt size, bolt strength, application
(permanent, non-permanent, etc.) and lubrication or lack thereof.
They don't vary on which half of the fastener is experiencing sliding
Correct, so _if_ one portion of the fastener (namely the bolt) _does_
have a friction load, the net torque applied will be low as compared to
For most relatively small bolts and applications, the effect is probably
minimal, granted, but the general principle holds.
No the torque spec will not be low. Both the nut and the bolt would
have frictional resistance on the underside if turned. See the
picture in this thread so you can see the symmetry of a bolted joint.
The placement of the threads doesn't affect the frictional symmetry.
Because he didn't read the original question??? :)
Choose the nut if you can. Again, if there's no side load on the bolt
(that is, it turns freely in the hole) there will be virtually no
difference. _IF_ (again, the proverbial "big if") there is a resistance
on the bolt, whatever that torque that resistance contributes is will
contribute to the reading of the torque wrench so the actual torque
applied to the fastener will be low by that amount.
In normal situations, again, as noted, this will be small, but it's more
consistent to stay w/ the nut end.
These are discussion groups. You make a new post and a discussion is
started. If your original post asks a question then (if you're lucky) you
will get some answers somewhere in the thread. However; having the
discussion branch off in other directions is part of the package. There is
no requirement that the conversation stick to your original premise.
If the hole is lined up with taper rods, then the bolt drops in and
there is no "side load".
From Bolt Science.com:
"Typically only 10% to 15% of the overall torque is actually used to
tighten the bolt, the rest is used to overcome friction in the threads
and on the contact face that is being rotated (nut face or bolt head).
Notice that it doesn't say anything about the side of the bolt being
squeezed by the hole. It seems that you're the one with your head up
Notice it says "typically"...
Notice I have continually used "if" for the cases where it is/can be a
problem and have also continually pointed out it isn't significant where
there isn't a problem.
In addition to the misalignment problem, there are also assemblies where
the bolt may, in fact, be designed to carry a load (as in a hanger, for
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