Abstract: A mechanism for locking together two mold sections includes one or more lock elements rotatably mounted on one of the mold sections, and a respective cylindrical tie rod for each lock element mounted on the other mold section. Each lock element has a cylindrical opening therethrough along its axis of rotation, and a plurality of lock balls disposed in recesses in the surface of the opening so as to form radially inwardly extending hemispherical projections on said surface. Each tie rod is of a diameter slightly less than that of the corresponding cylindrical opening in the lock element, such that the tie rod is axially slidably receivable within the opening. The surface of each tie rod has a plurality of longitudinal guide grooves radially aligned with the lock balls in the surface of the opening, and each lock ball is slidingly received in a guide groove when the tire rod is slidably disposed in the opening. Intersecting each guide groove at substantially a right angle is a lock groove.