Front Derailleur Clamp, Braze-on (28.6mm) - 17121
Most front derailleurs these days are sold as braze-on only since many modern hi (ugly) tech frames got weird shaped tubes that you can't get a clamp around. And the brazed-on plate on those frame limits you to whatever the frame designer thought what chainrings you should use (big mr tough guy chainrings only sorry too bad). Good thing your trusty steel frame doesn't have the lame braze-on plate. So use this simple, hinged, aluminum clamp adapter with any braze-on front derailleur. They're made in various sizes but we only sell the 28.6mm (1-1/8") size since that's the most popular steel frame seat tube OD. This slotted style is best in the case where a waterbottle boss gets in the way of ideal derailer height. The clamp can go above or below the braze-on and then you can fine-tune the height of the derailer using the slot.