When you're quoting a new injection mold, the mold base decision drives everything downstream — steel cost, machining hours, cycle time, and maintenance access. The two-plate (A/B plate) base remains the workhorse for simple open-and-shut parts, typically built on standard sizes like 200×200 mm up to 500×500 mm in LKM or Hasco footprints. A three-plate base adds a stripper plate for pin-point gating, letting you center-gate multi-cavity tools without a hot runner. In my shop, a 4-cavity three-plate tool usually runs 15–20% longer cycle than the equivalent two-plate, but you save on runner regrind and get better gate placement. Stripper plate and reverse stripper bases handle deep-draw cups where ejector pins would mark or deform the part. For undercuts, you're looking at slide cores or lifters — each slide adds roughly 8–12 machining hours plus fitting time, so factor that into your quote before the customer signs off.

Hot runner systems change the math entirely. A valve-gate manifold on a 4-drop tool can add $3,000–$8,000 in components alone, but it eliminates runner waste and cuts cycle time by 10–30% depending on wall thickness. Insulated runners sit in the middle — cheaper than full hot runner, but you need to watch gate freeze-off on thin-wall parts under 1.2 mm. Stack molds (two-level or three-level) double or triple cavitation without increasing tonnage, but the center section needs independent ejection and a reliable rotary or slide mechanism; misalignment there means flash and short shots. For high-volume packaging, a 2×8 stack mold on a 500-ton press is common. Whatever base you pick, leave room for water lines — a 12 mm baffle or bubbler in a deep core can cut cooling time by 20% versus straight drilling.

Don't spec a mold base from a catalog alone. Check plate thickness against injection pressure — a 300-ton press pushing 1,800 bar will bow a 25 mm A-plate over a 400 mm span. Use support pillars under the core plate, and always verify ejector plate travel clears the robot hand. If you're sourcing bases or comparing suppliers for a new project, visit MoldWorld (www.moldw.com) for mold sourcing info and vendor listings.