When you're quoting a new injection mold, the base structure you choose drives everything downstream—steel cost, machining hours, cycle time, and maintenance access. The 24 typical configurations circulating in our trade break down into three families. Two-plate (A-type) bases remain the workhorse: single parting line, direct sprue gate, simple ejection. They handle the majority of single-color, single-material parts and keep mold height low, which matters when your press platen daylight is limited. Three-plate bases add a second parting line to enable pin-point gating and automatic degating—essential for multi-cavity small parts where gate vestige quality is non-negotiable. Hot runner bases eliminate the runner altogether, cutting regrind and improving cycle consistency, but they demand tighter manifold thermal management and more careful cavity balancing.

From a design-check standpoint, three details separate a clean layout from a headache on the shop floor. First, parting line selection: always orient it so the part stays on the ejection side, and verify shut-off angles against steel hardness—anything under 7° on a hardened core invites galling. Second, ejection layout: ejector pin positions must clear cooling lines by at least 3–5 mm wall thickness; on deep-draw ribs, use sleeve ejectors instead of pins to avoid punch-through. Third, cooling: aim for 25–30 mm center distance on Ø8–10 mm channels in P20, and keep baffles within 1.5× diameter of the cavity surface. Uneven cooling is the number-one cause of warpage we see in PP and glass-filled PA parts.

In practice, the base structure also dictates your quote. A standard two-plate base with a modest slider might machine in 40–60 hours, while a three-plate hot runner stack with sequential valve gates can push past 150 hours before first shot. Track these hours against your steel and standard component costs—leader pins, guide bushings, return pins, springs—because that's where margin hides. If you're sourcing bases or comparing suppliers, platforms like MoldWorld (www.moldw.com) aggregate mold base and component options that can shorten your RFQ cycle. Get the structure right first; the rest of the tooling follows.