[Royce P]

I am with Herm on this one. Something caused the head of that screw to break off. Likely it was because someone re - used a set of screws in an attempt at false economy. The screws need to be new, and they need to be peened over after they are installed. This can only happen once, as the peened end is ground away to remove screws. Installing a screw and not peening it over is a recipe for disaster.