The Microshift M21 rear derailleur is designed for use with 6/7-speed Shimano Rapid-fire shifters and is built to be tough, durable and to provide smooth shifting. The long cage is suit for use with double and triple chainsets and offers excellent shifting thanks to the stiff steel construction. With steel bushes in the composite pulleys, this is a derailleur that is built to stand the test of time! If you want a great value 6/7-speed Shimano compatible rear derailleur, look no further than the Microshift M21!