sealing engagement with the nozzle of an injection molding machine not shown in operation resin flowing through bore 13 is introduced through aperture 14 and into flow passages or runners 16 of floating cavity plate assembly 20 for filling the mold cavities 18 therein the mold cavities 18 and flow passageways 16 are an integral part of the floating cavity plate assembly 20 which is releasably secured to plate 10 in well known manner such that the flow passageways 16 are in communication with the aperture 14 mounting posts 24 project outwardly from plate assembly 10 and slidably receive the floating cavity plate assembly 20 for ensuring accurate alignment between the plate assemblies 10 and 20 upon completion of a molding operation plate assembly 20 is separated from plate assembly 10 so that flow passageways 16 may be cleared of 34 runners 34 of hardened resin prior to the next operation a knock out side cavity plate assembly 26 see fig3 is also slidably received by guide pins 24 and is movable into precise aligned engagement with the floating cavity plate assembly 20 precision mating is ensured by the complementary mated male tabs 28 in plate assembly 20 and female tab receptive sockets 30 in plate assembly 26 see fig4 as shown in fig2 and 3 the plate assemblies 20 and 26 include complementary cavity halves 32 34 respectively of the part defining cavities 18 of the mold as shown in fig1 and 3 an elongated pin or core 36 is positioned in the center of each cavity 18 and extends axially therethrough when the cavity halves 32 and 34 are engaged to define the cavity 18 a core receptive bushing 38 is provided in each cavity half 32 of floating plate assembly 20 back plate.