If you really want screws and nuts to stay put, this works as well as cross threading or rust, and you can use a torch to undo it if you really must (cross-threading, not so much).

Works as advertised. This is not the first time I've used this product, and I will use it again. If it has a drawback, it is that you must put it in while installing the screw, nut, or bolt, because if you wait it will not penetrate threads. On the other hand, if you use it, don't expect to ever take the nut back off or the screw out of the threads. Cuz it just isn't coming out, not by your efforts, and not by vibration, and not by wear. This stuff works!!