The Lee Precision 6-Cavity Bullet Mold 357 Magnum blocks are machined from commercial quality aluminum and feature steel bushing and alignment pins. It is machined from aluminum blocks making them rust resistant. Aluminum molds heat up and cool down faster than iron or steel molds so good bullets can usually be produced after only a few casts. In addition, they are one-third the weight of iron or steel mold blocks for less fatigue during extended casting sessions. To ensure the best possible bullets, mold block halves are clamped together and then lathe-bored for unmatched roundness and size control. It comes with a cam operated, hard-anodized sprue plate which is held tightly with tempered spring washers at each end.