an apparatus and method for clamping a plastic injection mold . a first mold section is provided with a plurality of leader pins which protrude through apertures in a second mold section when the mold sections are brought into mating engagement to form a mold cavity . the second mold section is provided with cylindrical hydraulic cylinders having longitudinal passageways sufficient to accommodate the leader pins . each hydraulic cylinder is provided with a locking assembly capable of engaging grooves provided in the ends of the leader pins . once the leader pins have been moved through the second mold section and hydraulic cylinders the locking mechanisms engage the leader pins to allow the hydraulic cylinders to push against the locking mechanisms in an effort to clamp the mold sections together . by using a plurality of strategically placed leader pins and clamping assemblies , large clamping systems can be eliminated and more precise clamping pressures can be applied to the mold sections . since large prior art clamping systems can be eliminated , the size and weight of the present invention clamping system is substantially decreased .