On guns, I have only used them on the screws on the front sights, Jim. I had a Ruger .22 auto that I bought for my son and the first time we shot it, the screw from the front sight started to back out. I used the regular Locktite (red) and put it on the threads. It hasn't backed out since. I think the blue is more permanent, so it depends on whether or not you ever want to get the screw out again. We used a lot of it at the steel mill I worked at and I have only heard of putting it on the threads. I have never heard of putting it- only under the screw head. I will ask a machinist friend of mine, though and see what he says. Maybe someone else on here will know more than I. Good luck.
