Abstract: Injection molding takes place in a molding chamber which is formed between a core-defining member as part of a mold core assembly and a cavity-defining member as part of a mold cavity assembly. One removes a first mold core and mold cavity-defining member from the mold core and mold cavity assemblies when desired molding by means thereof has been accomplished, and replaces them with a new core-defining member and cavity-defining member to form a molding chamber of a different design. These are respectively secured to the remainder of the mold core assembly and mold cavity assembly, so that the main portions of the mold core and mold cavity assemblies may be retained in a mold press, and differing products may be manufactured.