The Shimano Ultegra RD-6600 rear derailleur for road bikes. This is an older model and at the time it was the second-best road derailleur in the Shimano line up right behind Dura ace. I’m not completely sure about production dates for this model, but the one pictured came on my 2008 Fuji Cross Comp. Still works great, it is light and for 10 speeds. Quick and crisp shifting, a high-quality component.