O.E.M. spacers typically wear out within a year of hard riding. O.E.M. wheel spacers should be checked and replaced as needed with every bearing service. Water and dirt act as a grinding compound between the seal face and the mating surface of the spacer. Once the grooves are deep enough, the sealing surface is lost, allowing water and dirt to pass through and contaminate the bearing. The All Balls Rear Wheel Spacer Kit contains a full replacement for your O.E.M. wheel spacer(s).