Worm on the string! For your thing! Not only does Dilbert make a good c-ring, but he also makes a nice bracelet if you're brave enough. And you know what they say, if you love it put a Dilbert on it.
This is the slim version for larger folks or those who enjoy a looser fit.
Slim size has a rough size of 2.5" in diameter outer measurement and a 1.75" inner diameter.