A mold closure assembly for a mounting press for mounting metallurgical specimens in a plastic mount including a cap lockingly insertable in the upper end of the mold, a conical member disposed in a mating conical recess in the lower end of said cap, spring means for urging said conical member into such mating relation, a compression member adapted for a sliding fit in the mold and handle means attached to the cap and foldable to a non-obstructing position to permit a temperature control unit to be attached to or removed from the closure assembly.