Lee molds are aluminum blocks, in permanently attached steel handles with sturdy grips. Aluminum blocks won't rust, lead won't adhere, and they heat quickly. But they are softer than blued steel and require gentle handling. If you treat these high precision molds with care and respect, they will last a lifetime. The cavity cannot rust. Cavity is finish pressed using a carbide ball, with 30 tons pressure. Sprue cutter leaves no stem. Now available in the smooth working SIX (6) CAVITY mold blocks: We recommend the #LEE-490-6C six cavity mold, which uses #LEE-HANDLE, and is the smoothest operating mold we've ever used. Make balls so quickly, smoothly, you can recover the cost of the six cavity mold in one evening!