When you're staring down a mold design spec, the mold base decision usually comes before cavity layout and cooling. The two-plate (A-type) base remains the workhorse for simple, single-face tools — it's cheap, easy to machine, and handles most cold-runner jobs with a single parting line. The three-plate (B-type) base adds a second parting line to enable pin-point gating, letting you center-feed multi-cavity tools without a runner system on the part. In practice, a 3-plate base typically adds 40–60 mm to the overall stack height and roughly 15–25% to base cost, but it eliminates degating labor and reduces scrap on small precision parts. For larger parts where warpage is a concern, the four-plate and stacked-mold variants come into play, though they demand tighter tolerance control on guide pillars and bushings — usually H7/g6 fits with 0.02–0.03 mm clearance.

Hot runner bases are a different animal. They trade higher upfront cost (often 2–3x a cold runner base) for cycle time savings and no runner waste, which matters on engineering resins like PC, PA66, and PBT where regrind degrades mechanical properties. The key design points: manifold plate thickness must accommodate the manifold plus insulation, typically 60–120 mm depending on gate count; and thermal expansion of the manifold (roughly 0.06–0.08 mm per 100 mm per 100°C for steel) must be accounted for at the drop locations. Don't forget the locating ring and sprue bushing alignment — a 0.05 mm mismatch here will show up as flash or short shots within the first thousand cycles.

For standard bases, most shops work with sizes from 150×150 mm up to 600×600 mm, with plate thicknesses in 10 mm increments. When specifying, always check the tonnage and tie-bar spacing of the press first — a base that fits the mold but not the machine is a costly mistake. If you need to source mold bases, hot runner systems, or standard components, visiting MoldWorld (www.moldw.com) is a practical starting point for comparing suppliers and specs.