Abstract: A locking device mounted in the interior portions of a mold includes a first member having an aperture therein adapted to be coupled to a first section of the mold, a second member having an aperture therein adapted to be coupled to a second section of the mold, the first and second members being alignable with one another so that the apertures therein can be aligned with each other, a pin being provided axially in one of the first and second members, the pin being radially compressible and being axially movable in the aperture in one of the members and being receivable in the aperture in the second of the members such that when the pin is axially moved into the aperture in the second section, the pin first compresses radially and then expands so as to be securely locked to the second member thereby locking the two members and the two sections of the mold together. A spring is preferably used to apply a force to keep the two sections tightly held together when in the locked condition.