It's a zinc based alloy called Zamac. It's used because of it's characteristics when molded in a die. It doesn't expand as it cools; it scrinks a very controlled and known amount. It was developed for tool amd die makers to make "mock-ups" of castings. "Zamac" is(was?) the trademark brand. I'm sure there are generic equivilents by now. It makes very precisely sized castings, so little or no machine work is needed on the parts. It's also realtively cheap, and that's important too, and it melts and molds at low tempatures for metals. You could melt it on a kitchen stove, just barely. It melts a little hotter than lead, maybe 700*F, no more than that. It's about a third the density of pure lead(too soft for most things). That help?
