Phil Wood mud guards are designed to help protect your Phil Wood bottom bracket cups from getting dust, dirt and mud that can accumulate in and around the bottom bracket cup splines. They are designed with a drain opening to allow any moisture between the bearings and mudguard to vent out. They are designed to install onto any Phil Wood square taper bottom bracket cup sets. Each set of mud guards comes with 4 rubber o-rings, (preinstalled and two replacement).