Provides a comfortable grip for holding cases during case trimming and chamfering sessions. Installs into all popular priming tools that accept priming tool shell holders including our Lee Auto Prime and Auto Bench Prime and others: K&M Sinclair FA Platinum or Perfect Seat CPS or 21st Century.This adapter holds your brass while trimming to the appropriate length or chamfering the inside and outside of the case neck. Allows you to rapidly change between pieces of brass without having to loosen up a knurled shell holder every time.