an injection nozzle assembly is used for molding a plurality of articles having accurate dimensions without causing a sink mark to appear in the molded article . the injection nozzle assembly comprises a body which is heated to a temperature higher than the melting point of thermoplastic material . a cylindrical bore is formed within the body , and an outlet port is formed at one end of said cylindrical bore . a plunger moves within the cylindrical bore between a first position near the outlet port to a second position which is remote from the outlet port . a first feed line supplies the molten thermoplastic material and a second feed line feeds high pressure through passageways that are formed within the body . the plunger is formed within a first passageway connecting the feed line with the outlet port when the plunger is moved to the second position . the pressure at the outlet port is reduced by the movement of the plunger from the first position to the second position .