The Shimano Altusm M310 8spds Rear Derailleur has light action operation and over-size pulleys for a wide gear choice Shimano Altusm M310 8spds Rear Derailleur Altus mountain bike rear derailleur with light action operation and over-size pulleys for a wide gear choice Oversize 13/15-tooth tension and guide pulleys to reduce noise and wear Extension spring and low-friction fluorine-coated link pivot bushing result in a light shifting action Top normal spring for use with Rapidfire shifters IG and HG chain, 7- and 8-speed compatible For use with 28 to 34 tooth low rear sprockets, total capacity 43 teeth