The Large Oi fits 23.8 – 31.8mm fits bars, while the Small Oi fits 22.2mm bars. 

Most of the time the area you’ll be attaching the bell to, will be either 22.2, 25.4 or 31.8mm and can generally be separated in to the below categories.

• Road Bike – Handlebars generally come in two clamp sizes 26mm (older style) and the newer ‘oversized’ 31.8mm. The area where you attach the Oi bell will most likely be either 25.4mm or 31.8mm.
• Commuter/Cruiser Bikes – Handlebar sizes do vary due to the wide variety of styles, however most bar sizes would be either 25.4 or 31.8mm
• Mountain Bikes – Handlebars generally come in two clamp sizes 25.4mm (older style) and the newer ‘oversized’ 31.8mm. On some bars there will be a bulge in the middle and the bars will thin out towards the brake levers. If you want to attach your bell here, then please make sure you measure as it could mean you move from a large sized bell to a small. For instance the grip area on some of these bars will be 22.2mm, whereas the bulge is 25.4mm.
• BMX – Always 22.2mm.

Tip:

• If your handlebar is any bigger than 22.2mm then you will need to choose the larger sized bell. The Larger Oi will come with shims that will allow you to attach the bell to bars 23.8, 25.4 and 26mm.
• If your handlebar in the middle looks ‘normal sized’, it’s probably 25.4mm.
• If your handlebar looks overly big in the middle, it’s probably 31.8mm.

For further info check out this great guide >> www.bikeman.com/bicycle-repair-tech-info/bikeman-tech-info/1637-handlebar-diameters.