A spring nut assembly is inserted within the internal cavity of a shank tube until the nut is aligned with opposing side holes in the side walls of the shank tube. The spring maintains the nut in alignment with the opposing side walls. A hitch pin including a threaded portion for engaging the spring nut assembly is inserted through the side holes of the receiver tube and the shank tube until the threaded portion of the hitch pin engages the nut mounted within the shank tube. The hitch pin is then rotated relative to the nut to clamp the shank tube against the receiver tube. A lock or clip can be attached to the end of the hitch pin to prevent accidental or unauthorized removal of the hitch pin from the receiver assembly. A bushing can also be used over the reduced diameter.