Um... it's brass...try to remember what tools you use to remove it , find the tools and maybe ...
find the mallet and search around ..........and did you have a box for any pieces of a canoe , maybe you put it in a wrongIt's maddening. I remember unscrewing the 4 screws in the ring, I remember holding a screwdriver blade against the inside of the brass and tapping with a mallet to remove it. But I can't remember whether I did it at the canoe or in the basement. Can't find it in either location. Maddening!
I don't know what diameter to make the hole in the fixture!