Chain, motorcycle, simplex, BS, steel, 12.7 mm pitch, Fenner.

Motorcycle chain has rubber o-rings built into the space between the outside link plate and the inside roller link plates. The o-rings are included as a way to improve lubrication to the links of the chain, a service that is vitally important to extending their working life. These rubber fixtures form a barrier that holds factory applied lubricating grease inside the pin and bushing wear areas. Further, the rubber o-rings prevent dirt and other contaminants from entering the chain linkages, where such particles would otherwise cause significant wear.