SHIMANO RD-M640 Zee Shadow Plus 10 Speed Rear Derailleur Shadow Plus technology keeps the low profile shape reducing chainstay and other contact, and adds a chain tensioning device reducing noise and dropped chains Compatible with Dyna-Sys 10 speed Shimano products Aluminum construction with sealed bearing pulleys 4 fluoric coated link pivot bushings for smooth operation Shimano Reference Number: RD-M640