The standard focuser from Moonlight only has the one dovetail for the finders I believe. The dual rate focusers have the added fine focusing ability and the twin dovetails for the finders. I could be wrong, but I believe that is how it works.

I had to take a hacksaw and cut off the lip of metal that was on the finder stalk to allow it to fit the Moonlight focuser. Otherwise, it would not fit.