Bulldog gooseneck couplers are quick and easy to engage and strong and secure on the road. Our unique, patented, extruded locking plate design and high-strength steel components make Bulldog Gooseneck Couplers 65 percent stronger than similar products. Coupler includes 4-1/2 inch diameter outer tube, 4 inch diameter inner tube with cast locking plates, 3/4 inch load bearing pin and single set screw.