A preform mold (100) including a core plate (210), a cavity plate (410) and a plurality of mold stacks (MS) mounted between the core and cavity plates (210, 410). Each mold stack (MS) includes a core insert (250) mounted to the core plate (210), a cavity insert (440) mounted to the cavity plate (410) and split mold inserts (350) mounted between the core and cavity inserts (250, 440). The core inserts (250) are mounted to the core plate (210) by fasteners accessible from a rear side of the core plate (210). When the mold (100) is assembled, the core inserts (250) can be secured by the fasteners in a fixed condition in which they are immovable relative to the core plate (210). Also disclosed is a method of aligning the core inserts (250) by securing the core inserts (250) from a floating condition, in which they are able to slide relative to the core plate (210) along a sliding interface therebetween, to the fixed condition.