DID ERVT Series Heavy Duty Narrow X Ring Chain in Gold, Motocross Enduro Chain The DID 520 ERVT Narrow Enduro Racing Narrow X-Ring Chain gives you the durability of an X-Ring chain in a width as skinny as non-sealed chains. If your bike has slim clearances designed for traditional, non-sealed drive chains, DID’s ERVT is a great choice for getting the extended durability of their X-Ring chain in a narrow package. The ERVT uses DID’s patented X-Ring design to hold lubricant inside the chain assembly and reduce friction points that occur in every link. This makes the ERVT specifically geared for the harshness of off-road riding with 1.5 to 2 times the lifespan and half the power loss of competing O-ring and modified O-ring designs.