This is a DuBro 4 Pin 1-1/2" Spinner. These are made to be simple, easy and safe to install. Featuring a unique insert lock design for attaching the back plate and spinner - giving a solid and secure hold. Each spinner comes complete with five shaft adapters (5mm, 6mm, 1/4", 7mm, 5/16") so you don't have to drill out the back plate. Package includes one spinner and five shaft adapters.