Sram jockey wheels xx x0the sram black box ceramic derailleur pulleys are made of the same material as the standard pulleys but they use polished stainless steel races and ceramic ball bearings in a sealed unit the pulleys are a bit lighter and more durable thanks to the ceramic balls but more importantly they have substantially less drag than standard stainless steel balls and they can be taken out and re lubed if your heart desires these pulleys should outlive your bike provided your