I actually bought these for my 6" Skywatcher Refractor. I was going to use one of them assist with a balance issue, but since changing to moonlite focuser, I didn't need the rings anymore.
I have fitted one of the rings to the scope in the photos attached. The ring is the one closest the focuser. They are very tight fit - you can see the "jaws" don't completely close, but they do fit. They also come felt lined so they don't mark the scope.