30,000 lbs Gross Trailer Weight Durable Black Powder Coat Finish Fits Standard Trailer Goosenesck Coupler Tubes Gooseneck king pin adapter, changes your gooseneck trailer to a 5th wheel trailer. Standard king-pin with 10" bolster plate fitted to 18" long 4" rnd. (GN5), 4 1/2" sq. (GN6) or 4" sq. (GN7) extra heavy wall tube. Pull your gooseneck trailer with a pick-up or semi-tractor.