Hope 61801 2RS Rear MTB Hub BearingA hard-wearing bearing for use with a variety of moving parts on your bike, this 61801 2RS model features internal balls and lifelong lubrication for an efficient performance and low maintenance. With a double-sided rubber seal, it keeps out dust and dirt to ensure top performance through the most challenging conditions. Features: Material: Steel Bearing Type: 61801 2RS Inner Diameter: 12mm Outer Diameter: 21mm Width: 5mm Seal: Double-sided rubber seal Buy Hope Wheels & Tyres from Chain Reaction Cycles, the World’s Largest Online Bike Store.