A split mold insert for defining a relief portion of a molded article, comprising: a body defining a mold cavity for the relief portion of the molded article , the body having a male projecting portion with a shutoff face , the shutoff face for selectively defining, in a molding configuration of the split mold insert, a parting line with an adjacent mold stack component and, in a cleaning configuration of the split mold insert, a molding surface, the male projecting portion having a frustoconical outer surface configured to cooperate with a female receptacle associated with the adjacent mold stack component to provide a melt barrier in the cleaning configuration of the split mold insert, the body being split into a plurality of split mold insert parts that are separable in a separation dimension (L) for ejection of the molded article, each split mold insert part having a mating face for mating with a complementary mating face of an adjacent one of the split mold insert parts, the mating face having an inner face region adjacent to the mold cavity, an offset , and an outer face region on an opposite side of the offset from the inner face region, wherein at least a part of the inner face region terminates at the shutoff face of the male projecting portion, wherein the offset of the split mold insert part is configured to cooperate with the offset of the adjacent one of the split mold insert parts to prevent melt from passing between the offsets and to guide melt towards the melt barrier, and wherein the offsets are parallel to the separation dimension (L) such that the offsets slide relative to one another with no change in their separation distance (D); characterized in that each offset terminates at the frustoconical outer surface of the male projecting portion and the dimensioning of separation distance (D) allows air, but not melt, to pass between the offsets so that the offsets collectively define vents on either side of mold cavity over their entire lengths. a body defining a mold cavity for the relief portion of the molded article , the body having a male projecting portion with a shutoff face , the shutoff face for selectively defining, in a molding configuration of the split mold insert, a parting line with an adjacent mold stack component and, in a cleaning configuration of the split mold insert, a molding surface, the male projecting portion having a frustoconical outer surface configured to cooperate with a female receptacle associated with the adjacent mold stack component to provide a melt barrier in the cleaning configuration of the split mold insert, the body being split into a plurality of split mold insert parts that are separable in a separation dimension (L) for ejection of the molded article, each split mold insert part having a mating face for mating with a complementary mating face of an adjacent one of the split mold insert parts, the mating face having an inner face region adjacent to the mold cavity, an offset , and an outer face region on an opposite side of the offset from the inner face region, wherein at least a part of the inner face region terminates at the shutoff face of the male projecting portion, wherein the offset of the split mold insert part is configured to cooperate with the offset of the adjacent one of the split mold insert parts to prevent melt from passing between the offsets and to guide melt towards the melt barrier, and wherein the offsets are parallel to the separation dimension (L) such that the offsets slide relative to one another with no change in their separation distance (D); characterized in that each offset terminates at the frustoconical outer surface of the male projecting portion and the dimensioning of separation distance (D) allows air, but not melt, to pass between the offsets so that the offsets collectively define vents on either side of mold cavity over their entire lengths. <EOS>