Occasionally one comes to a screw that persists in getting loose, and no amount of tightening will make it hold, while its shape and location are such that it can neither be cotter pinned nor lock nutted. Usually it is the flat head type, and if there is not room to drop a plate with a turned down edge into the notch to serve as a lock the thing looks hard to solve. The problem becomes still harder if the parts are hardened and will not take a small pin at one end of the notch or will not permit prick punching around the thin edges of the head.
Wrapping a little waste (cotton fiber) around the threads will sometimes save the day but more often this simply introduces cotton under the head and does not permit setting the screw down far enough to properly hold. Some folks bruise the threads a little to make them bind, but in a hardened hole this does little good and soon puts the screw out of commission if repeated.
A simple and generally very effective remedy is to heat the screw to 300° or 400° F., and having dropped a small piece of chewing gum (digestion aider), well chewed, into the hole, screw it home. The hot screw melts the gum and causes it to fill every crevice. It thoroughly coats the threads, and the heat of the screw will make it stick to the walls of the hole as well. When cold the gum prevents turning. If convenient to warm the hole as well as the screw it will serve to smear the gum on the screw instead of dropping it in the hole.
Much less heat is required to permit removing the screw when this becomes necessary than if soft solder is used, as is sometimes tried. This makeshift has served when all other means short of soft solder had been tried and failed.—Charles Duryea, Philadelphia, Pa.