I was too lazy to paint my minis, so I adapted the Zombicide indentifier rings to work with the board game Mice and Mystics. I guess they also work with any other mini that has 20mm bases like Descent 2 I believe.
Anyhow most of them got a tight fit, some are a bit more loose, but still hold well. But Colin (red) for some reason doesn't have a 20mm base but 19mm base on my mini. If it's same with your mini, scale the ring down to 95.5% and it fits on him as well.