D.I.D. 520 ERV3 X-Ring Chain is the world’s lowest friction O-ring chain thanks to D.I.D’s patented X-Ring technology. The X-Ring’s four contact points reduce friction while keeping dirt out and lubrication in. D.I.D. 520 ERV3 Special patented heat treatment process produces 1.5 times harder pin. Gold finish throughout. Includes rivet link.