CURT X5 Gooseneck to 5th Wheel Adapter for Double Lock Hitches, Industry Standard Base Rails, 20,000 lbs Model 16210 57 1 4" The 1704420 Buyers Underbody Box Headache Rack Rear Ladder Rack Gull Wing Box Options:Gull Wing Box W Hex Headache Rack Only The 1704420 Buyers Underbody Box is one of the best underbody truck boxes for your money This particular model is designed to fit select years of the Ford F 150 (see application info to verify fitment) the adapter plate post simply mounts into the gooseneck trailer ball hole using a solid shank and is secured with the locking mechanism provided by the gooseneck hitch This CURT 5th wheel adapter plate features a round shank and is compatible with CURT Double Lock gooseneck hitches