This adapter is required for the use with the Thule 517 or 518 bike racks when also using the Thule Xsporter or rapid aero bars. Mounting hardwear for the 517 Peleton and 518 Echelon bike racks. Please consult the Thule Rack Finder to match the correct Thule parts with your vehicle 91021425095 26911400015 XADAPT9