Motorcycle Drivers Backrest - Black - 7" x 7" to Fit Corbin Seats Motorcycle Driver backrest for Corbin seats. Measures 7" x 7". This size is perfect for Harley's. Fits all Corbin and other seats that accept a backrest with a 5/8" square stem. Pad angle is adjustable and has 2 inches of foam padding under the vinyl cover for comfortable back support. We also carry a larger 10 x 12 size.