A mold stack (116, 216, 316, 416, 516), comprising: a core insert (120, 320, 420, 520), a core ring (140, 240, 340, 440, 540), and a split insert that are configured to cooperate, in use, to define a molding cavity; the core insert (120, 320, 420, 520) defines a ring seat (192, 392, 492) on a medial portion thereof upon which the core ring (140, 240, 340, 440, 540) may be seated, in use, in cooperation with a mounting interface (190, 390) thereon; the split insert defines a pocket that extends coaxially through a second projecting portion thereof within which to receive a projecting portion of the core ring (140, 240, 340, 440, 540); the core ring (140, 240, 340, 440, 540) and the split insert being further configured to define a core ring-to-split insert parting line that is within the pocket of the split insert; wherein a top portion of the molding cavity is split between the core ring (140, 240, 340, 440, 540) and the core insert (120, 320, 420, 520); wherein an inner surface of the core ring (140, 240, 340, 440, 540) defines a core ring-to-core insert split line in cooperation with an outer medial surface of the core insert (120, 320, 420, 520); wherein the core ring (140, 240, 340, 440, 540) defines a split line vent that is configured to cooperate, in use, with the core insert (120, 320, 420, 520) along the core ring-to-core insert split line for venting, in use, air from the molding cavity; and characterized in that the core ring (140, 240, 340, 440, 540) defines a branch conduit (141, 241) that is configured to fluidly connect the split line vent with a trunk pressure conduit that is associated with at least one of the core insert (120, 320, 420, 520) and a lock ring (130, 430) of the mold stack (116, 216, 316, 416, 516) a core insert (120, 320, 420, 520), a core ring (140, 240, 340, 440, 540), and a split insert that are configured to cooperate, in use, to define a molding cavity; the core insert (120, 320, 420, 520) defines a ring seat (192, 392, 492) on a medial portion thereof upon which the core ring (140, 240, 340, 440, 540) may be seated, in use, in cooperation with a mounting interface (190, 390) thereon; the split insert defines a pocket that extends coaxially through a second projecting portion thereof within which to receive a projecting portion of the core ring (140, 240, 340, 440, 540); the core ring (140, 240, 340, 440, 540) and the split insert being further configured to define a core ring-to-split insert parting line that is within the pocket of the split insert; wherein a top portion of the molding cavity is split between the core ring (140, 240, 340, 440, 540) and the core insert (120, 320, 420, 520); wherein an inner surface of the core ring (140, 240, 340, 440, 540) defines a core ring-to-core insert split line in cooperation with an outer medial surface of the core insert (120, 320, 420, 520); wherein the core ring (140, 240, 340, 440, 540) defines a split line vent that is configured to cooperate, in use, with the core insert (120, 320, 420, 520) along the core ring-to-core insert split line for venting, in use, air from the molding cavity; and characterized in that the core ring (140, 240, 340, 440, 540) defines a branch conduit (141, 241) that is configured to fluidly connect the split line vent with a trunk pressure conduit that is associated with at least one of the core insert (120, 320, 420, 520) and a lock ring (130, 430) of the mold stack (116, 216, 316, 416, 516)