I have to be honest, this product just did not work for me. Beside being priced on the very high end as most Leica accessories are, the Finger Loop just didn't feel comfortable. A lot of the reason you shoot with a rangefinder is how everything feels, so you have to try this one out for yourself and make that decision. I went this a medium size loop, and it seemed about right.
You can pick one up here - Finger Loop for Handgrip M (Medium)
Ben Hider - Event Photographer based in New York City and Westchester