From the Velo Orange Website: "One of the characteristics of fine bikes is a lack of stuff clamped on all over. There are brazed-on fittings or integrated mounts for everything required.
I often take a busy bike path out of town on my rides, so I decided to mount a bell on my new bike to warn pedestrians and slower riders. Of course, I chose one of our lovely brass bells. But how to mount one without a clamp? The French constructeurs tapped the bike's stem and screwed in the bell. I wasn't willing to do that, so my solution was to make a headset spacer mount that the bell screws into.
Works with Temple bells or Japanese bells. Hardware is included, but bell is not. The spacer bell mount is 10mm thick.
Note: if you have an older bike with little room under the headset nut, then get a Retro Mount instead."