When I bought my Optilock ringmounts , they only sold one size, low. I don't know if that's still the case or not. The optilocks have the benefit of plastic inserts that will self center and they will never mark an expensive scope.
Some of the older two piece Optilock mounts had sucky soft screws. My Optilock Ringmounts bought about 3 years ago had good hex screws.
