Addtl info for part #4, not fully tightened. Part #3 can rotate in the steel bushing but the nylon part on the nylock nut is engaged so that it will not come loose. This hitch provides full range of motion: Yaw, Pitch and Roll. Pitch by function of the ball joint (though limited at some point), 360 degree yaw by the pin rotating in the ball joint, and 360 degree roll by the ball joint rotating in the steel bushing.