Spinners aren't specific to a particular engine size -- they are primarily a fit to the airframe, then fit to the prop -- the engine really doesn't come into it. For instance, I have a 3" spinner on a 46-size engine with one model & a 2" spinner on a 78 size engine with another model.

Since spinner manufacturers can't possibly know what your engine/airframe/prop combo will be, they simply make spinners with arbitrarily-sized holes & expect (quite rightly) that you will do the fit.

There are a couple of rules:

The prop blades shouldn't touch the sides of the spinner, or the rubbing/vibration could make either, or both, the spinner & prop fail.

A spinner shouldn't be larger than ~ 25% of the diameter of the prop blades, or you will start to lose prop efficiency -- eg. a 3" spinner is about as big as you want to put on a 12" prop. That isn't cast in stone, but it is a reasonable max size relationship.