The Auto Primer Tube is designed for use RCBS(R) 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(R) II and Reloader Special Presses. Note: Not for use with RC Supreme.