Shimano Ultegra 10 RD-6600-SS Rear Derailleur - Double

"Redesigned for 2005 with a new look and 10-speed capabilities. Precision shifting for narrowly spaced 10-speed cassette sprockets. 11-tooth pulleys alternate contact with chain links, reducing chain wear, and the larger pulley diameter runs smoother and lasts longer. Low-friction Advanced Light Action design reduces shifting efforts. Max. sprocket: 27TMin. sprocket: 11TFront difference: 14TTotal capacity: 29TWt: 209g."