The 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 chain is cleaned and replaced when it should, before the stretched gritty chain wears down the pulleys. Features: • The SRAM Black Box ceramic derailleur pulleys work with the 2008 SRAM X.0 rear derailleur. • The upper jockey wheel spins on a shaft that goes through the jockey cage pivot point. • Weight for the pair is 24g.