I assume that you are screwing the screw as far down as it will go, right? If that's the case then it's as simple as the screw that goes through the spinner is just too long. Use a dremel (or a hack saw if you don't have a dremel) and cut a little bit off of the end of the screw. This will give you enough room to completely tighten the screw down on the spinner, and keep it from slipping.

Hope this helps

Ken