Rivet Type Connecting Link for D.I.D 520ERV7 Chains. Gold Finish. The D.I.D ERV7 X-ring chain is the ultimate high-performance, lightweight, low-friction sealed ring race chain available. An improvement from the ERV3, the ERV7 boasts lots of upgrades, including an 11% longer chain life. D.I.D has upgraded the materials of the pin, bushing, inner/outer plates, and the patented X-Ring seal, increasing wear resistance and reducing friction.