How do you figure out what size spinner you need for a prop?

whatever the plans show, or what looks good and fits the prop without to much whittling on the prop holes,lots of planes don't have spinners.

RcBBQ - (hope that is not a prophecy of what happens to your plane! Is that anything like "my plane....it's toast now"?)

I think the spinner is pretty much cosemetic. The plastic ones look terrible after just a while with the electric starter cone rubber and are sometimes short lived. Aluminum is kool but often I just use a Highley hub or Dubro cone shaped hub nut. Look neat, safe and last.... even through accidents!

RcBBQ,

The spinner size is regulated by the model and not by the engine or prop. Because of this, the holes in the side of the spinner that go over the prop are usually cut to fit the smallest prop that the MFG thinks will be used with that particular spinner. Therefore, you will find that in most cases, you have to enlarge the holes for the prop.

So, if I were to enlarge the holes, I will also need to balance the spinner? Also, will it be OK to enlarge the holes on an aluminum spinner? Oh, one more question. Can you recommend a balancer for spinners?
Thank you,
Kevin