The Rollerboys will make your bike ride so smooth that you will never stop anymore! The composite material is strong and durable and the special teeth pattern makes sure you can shift to a higher gear with the speed of light! High quality pulley wheels are a must have for every serious bike rider, with the RollerBoys you are good to go!Features:- Narrow Wide tooth profiling ensures ultimate chain retention- Composite material provided by EMS Swiss, with 40% glass-fiber mixture- Sealed bearings- Compatible with SRAM 1X11Specifications:- Compatible with brands: SRAM- Part materials: Grivory EMS- Gears: 11-speed- Bearings material: CrMo- Narrow wide i: Yes- Pulley size: 12TTechnology:Narrow/Wide:- Narrow Wide tooth profiling ensures ultimate chain retention.