Protects rear derailleur by maintaining chain tension when the rear wheel is removed Ideal bike service tool for washing, tune-ups and traveling Accommodates road bikes, cyclocross bikes, mountain bikes, electric bikes, fitness bikes and more Fits standard 9mm Quick-Release style dropouts Fits 12mm Thru-Axle dropouts Prevents the chain from slapping against delicate and painted frame surfaces High-density Delrin roller is easy on your chain, yet incredibly durable CNC machined aluminum body is corrosion-resistant and comfortable in-hand Tool-free, single-hand design makes use simple and effective for beginner or professional bike mechanics