It's for road bikes with a normal-for-road-bikes 26mm handlebar center. All of our Nitto drop bars and Moustache H'bars, and most others. Keep in mind that the other bells go onto 22.2mm handlebars--basically, the grip area of Albatross, Dove, and Most Mountain Bike bars---and all of our stem quills.
But if you want to put those bells onto bigger parts of handlebars, they won't fit.

The accompanying pictures show a few reasonable possibilities.You may discover more!

Anyway, we like bells, we especially like these Japanese brass ones, and we're happy to have this one, which fits bigger bar sections.  Probably it'll do fine anywhere on a drop bar. Secret tip: The Bell 26's clamp has another slot that lets it work perfectly on a 22.2mm bar, too.

Nonsecret tip: The best way to rig it: On the sleeve of the bar (or over the twine). Use slip-jaw pliers to squeeze the clamps together--it just makes it easier to use the screws.

Also note: The dome is rivetted to the shaft; the shaft itself is threaded. What's that mean? Thanks for asking: It means you can unscrew the dome-with-shaft from the clamp and THEN, if you have a threaded stem or headset spacer, you can thread the shaft-and-dome directly into it, thereby end-arounding the clamp. The other bell we sell, the slightly bigger & louder "hammer striker" model (31-467) doesn't allow this. Which is no reason not to get it if you weren't going to do that anyway.