CURT X5 Gooseneck to 5th Wheel Adapter for Double Lock Hitches, Industry-Standard Base Rails, 20,000 lbs Model 16210CURT X5 Gooseneck to 5th Wheel Adapter for Double Lock Hitches, Industry Standard Base Rails, 20,000 lbs Model 16210 CURT 5th wheel adapter plates are a fast, dependable way to convert your gooseneck trailer hitch into a set of 5th wheel rails to accept a 5th wheel hitch and switch back again. With gooseneck installation brackets and a gooseneck hitch already mounted, the adapter plate post simply mounts into the gooseneck trailer ball hole using a