These are pins that go through the top clamp plate into every plate with one pin offset to keep the plate from being assembled incorrectly. The pins are also used to guide the mold back together after the mold opening during the cycle. The pins serve two purposes. One is to guide the mold back together without misalignment. Without them there could be a possibility that the core and cavity would hit upon closing and cause damage the steel. Leader pins also prevent the mold halves form being assembled 180 degrees. This is why the offset pin is used on what mold makers call the zero corner.