Simple, easy and safe to install (no need to use the palm of your hand). The spinners are available in 7 sizes. Each spinner comes complete with 5 shaft adapters (5mm, 6mm, 1/4", 7mm, 5/16" shafts). You don't have to drill out our back plates! 
Features a unique nylon insert lock design for attaching the back plate and spinner - giving a solid and secure hold. Designed with safety in mind.
Use Allen Wrench size 7/64" (not included)