When you're staring at a part print and trying to lock down a mold base, the first decision is almost always two-plate versus three-plate. A standard A/B plate two-plate base handles the majority of single-face parts, but the moment you need a center gate or multi-cavity balance with a cold runner, a three-plate base with a stripper plate becomes unavoidable. The 24 typical structures break down into families: two-plate (A-type, B-type), three-plate, hot runner, stack molds, and split-cavity designs. Each has a fixed plate sequence and guide-pin layout that dictates your ejector system. For example, a three-plate base needs a positive runner stripper plate return, often via a latch lock or spring-loaded puller, or you'll smash the runner on the next shot. In practice, I've seen more tool damage from missing that detail than from any steel selection mistake.

Hot runner bases add another layer. You're no longer just picking plate thicknesses—you're sizing manifold pockets, nozzle drops, and thermal expansion gaps. A typical 8-cavity hot runner base for a 150-ton press might use a 350×350 mm base with a 25 mm manifold plate and 0.02–0.03 mm expansion clearance per 100 mm of manifold length. Stack molds double your cavitation without changing the press, but the center section needs its own ejector and often a rotary union for cooling. The 24 structures also include unscrewing molds for threaded parts, where a rack-and-pinion or hydraulic motor drives the core rotation—those bases need a thrust bearing plate and a positive stop. If you're designing a mold base for a 500-ton press, don't overlook the locating ring and sprue bushing alignment; a 0.1 mm mismatch will flash the sprue every cycle.

Bottom line: pick the base family first, then verify plate thickness against injection pressure and support pillar placement. Add wear plates on the leader pins if you're running glass-filled resin, and always check the ejector plate travel against the knockout bar pattern. For more mold sourcing and base standard references, visit MoldWorld at www.moldw.com.