The Neck Expander Die expands the neck and flares the case mouth in a single step. This operation is critical to the successful reloading of cast bullets. This is an expander plug only, to be used with the body die, product 735-718. Notes:Replacement part for RCBS neck expander dieThis is the expander plug onlyThe complete die consists of a neck expander plug, plug rod and expander bodyNumber in the description refers to the diameter of the bullet used in the cartridge