The AMP Research BedXTender HD Tonneau Spacer Kit is useful for trucks with a tonneau cover that mounts to rails on the inside of the truck's bed. This kit may be needed to provide additional clearance in between the tonneau cover rails and the BedXTender to allow full use of operation. It is simple to use, just use the provided hardware to mount the spacers where the BedXTender would mount. Then, adjust the width of the BedXTender to fit with the spacers installed. Again, this kit is for use with tonneau covers that mount inside the truck bed.