Heavy duty Hone M600 all-mountain rear derailleur medium cage with unique Freehub axle mounting system for added durability Designed to absorb accidental impact without affecting shifting potential Revolutionary mounting system fixes rear derailleur to hub axle Alloy body & outer link leads to lower weight without compromising strength & durability Two fluorine-coated link pin bushings make this one of the slickest shifting derailleurs on the trails Top normal spring uses the spring to select higher gears&44; best suited to use with Rapidfire shifters Cable tension saver prevents impact generated tension within shifting system Must be used with FH-M600 Freehub Average weight 405 grams