The Auto Primer Tube is designed for use RCBS Automatic Primer Feed, which drops primers one at a time into the primer plug and sleeve. It helps stop misfires, as greasy fingers never need to touch primers, and the nylon primer pick-up keeps primers from falling out. It has a tube capacity of 100 primers and fits the Rock Chucker II and Reloader Special Presses. NOTE: This item is not for use with RC Supreme.