Shimano only produces the Di2 front derailleur in a braze-on option. So you will need this adapter is required to install your Di2 front derailleur to your frame if it does not have a braze-on hanger.
The Shimano engineers made it somewhat easy for us by designing only two clamps instead of the standard three. One is a 31.8mm clamp with adapters/shims to make it work with 28.6mm diameter seat tubes. The other size is for 34.9mm diameter seatubes. On a cosmetic note - the black anodization looks fantastic and matches the rest of the Di2 components. This clamp only works with Di2, it will not work with standard front derailleurs.