The zinc plating on our ball combo for the Rapid Hitch does scratch through to the base coat and eventually to the raw steel as the metal coupler of the trailer rubs the ball combo through normal use. To prolong the life of a combo ball we recommend the use of greasing the top of the ball which lubricates the coupler of the trailer. The best option for those who want a complete rust-free unit is to use our Greaseless Alumiball which is an aluminum ball combo with black caps on which allow the coupler to rotate freely without the metal on metal grinding. Below is a picture of a Rapid Hitch with the greaseless combo ball.