I am so impressed with this ring - it's SO cute! I love bats (in fact, I'm obsessed), so when I saw this ring I had to get one. I had no idea what finger I was going to wear it on, and after testing a few fingers I was so happy it fitted my thumb the best, I really wanted a new thumb ring too. The approximate diameter (before any adjustment) is; 17mm. I have worn this ring a few times and my thumb has not turned any strange colour, and the ring had gained no chips. It's still as good as new. I also bought the other bat ring from this shop which is larger in size but just as cute. I Love it!