There are two things you can count on with steel frames: they ride like butter and you'll have to spend an inordinate amount of time hunting down a braze-on mount in order to attach any of today's front derailleurs to them. Shimano's Di2 derailleurs are a good case in point, but the Dura-Ace FD-R9150 Front Derailleur Adapter simplifies the hunt. It's an age-old solution to a contemporary problem. Frankly, Di2 front derailleurs are designed to be attached to carbon frames whose seat tubes have such tortured, overwrought shapes that no clamp known to human kind can tame them, so they're all just braze-on derailleurs that mount directly to the frame. This rules out frames with traditional, round, tube-shaped tubes--unless, that is, you've got the right adapter. The FD-R9150 Adapter lets you marry the latest drivetrain technology with your favorite frameset.