Groundman, you don't have to use a 2.5" spinner just because the old one was 2.5" You can really use most any size that looks good. Well, within reason. You probably wouldn't want one that is 6" across! But I imagine you could use a 3 or 3.5" if you wanted to. Maybe a bigger spinner would have the flat space you need. You could take your plane to your hobby shop and try on some different sizes and types even!