It's supposed to be snugged down to the point that the arm just falls when you let it go, but not so much that it swings at the bottom of the movement. The nut itself shouldn't be able to back off, as it's one of those with that plastic locking insert inside. Too much looser than that, and you'll get a rattle upon the shot -- and that's defeating one of the purposes of this rest, which I still think is the quietest on the market, in my opinion.