Primer arm assembly

The primer arm slips into the slot in the ram. The little hook on the arm catches on a pin that is in the slot. Now as you raise and lower the ram, the primer arm pivots in and out of the slot. The cup on top of the primer arm is where a primer is placed when it tips out toward you. Then as you lower the ram it pivots into the slot and then comes up through the center of the shell holder. If there is a shell in the shell holder, this is where you press the primer into the primer pocket.