The Cage Guard is designed to add a layer of protection to your derailleur pulley cage to help prevent costly damage caused by rocks and debris. By limiting impact damage, the Cage Guard helps maintain smooth shifting performance and keeps your high-end derailleur in top condition.XT 8100 Model compatible with long-cage (SGS) Shimano XT 8100 rear derailleurs (does not work with 8150 Di2 models)Cage Guard is made from durable, low-friction Delrin thermoplastic, designed to withstand normal impacts and glide over rocksHelps to protect rear derailleur cage from damageCage Guard includes rust resistant stainless steel hardware MRP Cage Guard Miscellaneous Rear Derailleur Part UPC: 702430224444