If you are talking about an adaptor for a fiver to tow it with a goose neck ball, be carefull. I (and some others I have heard about) found that that can really damage the structure of some fivers. It sure did mine!!!
The "turnover ball" system looks like it would not have the same effect, but I have not tried it. I used the Cody hitch, and within a couple thousand miles, I was pulling the kingpin right out of my fiver. Some way it puts much more stress on the junction of the king pin box and the frame of the fiver.
Vaughn