Well Jim, I plan on replacing the steaming light. It is about half way up the mast. There are multiple holes where it was moved or the screw broke and was never taken out.
So I am going to drill out the old screws and fill with aluminum putty. Going to also fill in all the other holes around that light. Didn't want to push too much putty in the hole because it might damage an internal halyard. I don't think it will but don't want to take a chance. I will knead the putty and flatten it out to about 3/16" and then push it in with even pressure. Then remove any excess on the outside.
That is why I was asking about the mast wall thickness. Yeah, I can measure it when I get up there, but just preparing mentally ahead of time.