This is a manufacturer sourced replacement part designed for use with Chicago Pneumatic ratchet/wrenchs. This o-ring provides an air-tight seal for the valve. Over time this o-ring will shrink, become brittle and crack allowing for air leaks. At that time it should be replaced. It is made out of rubber and it is sold individually. Replac...Read moreing this item you would need hex key/allen wrench and pliers to replace this item.