These backing plates were designed for the DIY guy and professional in mind. The flex edges allow the backing plate to be more forgiving while buffing and they fit our 6" foam pad line along with our 4" foam pads for the dual head polisher. The 600Y & 500Y are great for our 6.5" & 5.5” foam pads. The 350Y plates are replacement plates for the dual headed polisher and the 300Y is a unique and versatile plate with interchangeable adapters; one makes the plate a drill chuck backing plate and the other makes it a pneumatic backing plate.