This spacer kit goes on the axle in between the inboard rotor clamp and side bell. It will keep the rotor from sliding over and rubbing the caliper. This has happened to everyone at one time or another. This kit is the perfect length for the Wilwood SA Stainless Inboard Kit. We have used this for years on our own car as it is cheap insurance. It can save you hundreds of dollars and keep you from dropping out of a race. Only weighs 2 ozs.