/diy/ - Do It Yourself

I've got a watch bezel, and I want to make it thinner. For the top this is easy enough, I can just find a flat surface and sand it down 1mm. But what do I do about the internal cavity where the bezel insert rests?

I could just make the insert thinner but I might want to go even lower. Buy a piece of round stock the right size and stick sandpaper to it to ream out the inside? Obviously, I can't remove any material from the bottom or the way it rides on the clickspring will be compromised.