~99% of new bikes sold today use 31.8mm or 35mm handlebar clamp diameters, so our stock Quick Release Handlebar Mounts included with Detour and Evo fit those two sizes out of the box. Of course, it's the bike industry, so these new standards evolved from older smaller diameters that are still used on some bikes today, so we have shims for 25.4mm and 22.2mm handlebars available, and if you're unsure of what you have, just shoot us an email and we'll make sure you get what you need!