Details M21 rear derailleurs are designed to work with 6- and 7-speed Shimano road and mountain shifters. Enjoy the wide variety of bikes you can get going again with M21 rear derailleurs.- Robust composite and steel construction- Compatible with Shimano 6- and 7-speed mountain and road systems- Long cage for double or triple cranksets and 32T max cassette cog- Includes frame hanger attachment for use with older frame designs