Abstract: A stack mold stabilizer for causing the multiple mold plates of a stack mold to maintain their required even spacing at all times during operation. The stabilizer includes a rack and pinion mechanism for maintaining an equal distance between the mold plates of the stack mold. The stack mold includes at least three mold plates with the mold plate at one end being fixed and having a first rack gear fixedly mounted to its side. The center mold plate has a pinion gear rotatably mounted thereon. The teeth of the pinion gear are maintained in firm meshing engagement with the teeth of the first rack gear by a first idler roller mounted on the center mold plate. The third mold plate has a second rack gear fixedly mounted to its side and has teeth which are kept in firm meshing engagement with the pinion gear by a second idler roller mounted on the center mold plate.