The Bulldog BX1 coupler is the result of generations of design expertise and field experience. If incorporates innovative features that revolutionize the benefits available from a gooseneck coupler and offers flexible mounting options with its Next Generation locking plate coupler mechanism. These features combine to make hooking up, adjusting vertical height and disconnecting quick and easy. The Next Generation coupler design operates easily with one hand thanks to the new locking handle design, and maintains smooth operation over time with grease fittings for every important operating part. Coupler includes 4-1/2 inch diameter outer tube with 2 set screws, 4 inch diameter inner tube with cast locking plates and 3/4 inch load bearing pin. Please Note: Requires welding of outer tube to trailer frame.