It’s a rubberized bit with a safety band that you feed your stretchy Garmin Forerunner (or similar, I suppose) watch band through and secure to cinch the whole thing tight on your handlebars.

I used this with my Forerunner 945 for a handful of months, even starting my Randonneuring career with it and completing a few 200k’s and a 300k – maybe a 400k as well. I think it was the 600k that my watch froze up trying to load the combined route so I got a dedicated bike computer (shoulda just learned to split the file or gotten the split files from someone but I was new, oh well).

Anyhow, it’s a super simple super niche bit of kit. Buy it please.