Apparatus for controlling the rate of flow of fluid material through an injection molding flow channel leading to a mold cavity, the apparatus comprising: a pin having a longitudinal length being adapted for back and forth axial movement through the flow channel; the pin having a protrusion at a selected position along its length, the protrusion having an upstream end and a downstream end and a maximum diameter circumferential surface intermediate the upstream and downstream ends; the channel having an interior surface area portion which is complementary to the maximum diameter circumferential surface of the protrusion of the pin; and the pin being slidable to a position within the channel such that the maximum diameter circumferential surface of the protrusion forms a seal with the complementary interior surface portion of the channel to stop flow of the fluid material.