A locking device for a mold including more than one movable plate. A spring-biased wedge block includes a first side wall and an opposing second side wall that is beveled with respect to the first side wall. A latch bar includes an inclined latch end for engaging with the second side wall of the wedge block. A cam bar includes a cam end for engaging with the first side wall of the wedge block. At least one of the wedge block, the latch bar or the cam bar is formed of a 4340 steel alloy, and at least one of the latch end, the cam end, or the wedge block second side wall is nitrided or nitride coated.