If you own several trailers it is usually easy to change the coupler on the trailer so that all trailers use the same size ball and new couplers for smaller trailers without brakes run about 20.00 at many locations.
I had an older jon boat trailer that was set up for 1 7/8" ball and all of my other trailers were for a 2" ball. It was cheaper and simpler to switch the coupler on the trailer to a 2" than have to change balls everytime I towed a different trailer.
Just another option.