This Spacer Plate is specifically designed to fit the new 320 and 400 model teardrop trailer frames. It builds up the space where the rack won't sit neatly on due to other bolt heads. Includes longer bolts to go all the way through to the trailer frame. Spacer is 1/2 in thick. This is just in case you bought your Jack It Bike Rack from another source that doesn't have this plate included. We do include this spacer with the Jack It Bike Rack if you buy it from us.