How much play should there be in a truss rod

[Michaelgsaid]

I’ve noticed that often I’ll have a handful of Allen wrenches that similarly fit into a truss rod not but they all have a tiny bit of play or movement when inserted maybe like 5% if you were looking at it at like a circle I wonder how much this is normal vs how much of it is something that can cause problems. I probably should be using a caliper to measure the truss rod opening and the Allen wrenches sizes that im using. I just don’t want to strip out any truss rods by using a wrench that is slightly too small.

[Mick Bailey]

A tiny bit of slack is usual, but sometimes the hex in the nut is oversize or has been worn round by using an Allen key that was too small. If there's too much slack I run through my collection, as sometimes an imperial key will be a better fit in a metric nut, or vice-versa. Sometimes where there's no good fit and the nut is tight I use a Torx bit that will sometimes engage better with the corners of the internal hexagon. I usually remove the nut and replace it if there's any doubt. The danger is that where there's too much slack the key can rotate in the hex just at the point where the rod is getting to the required tension - this can make removal difficult. Taking off the nut and lubricating the threads with dry film PTFE means an easier time when tightening up.