Strongly recommended for Shimano Front Derailleurs with Toggle Construction (e.g. RD-R7000, FD-RX810 current generation 11-speed and 12-speed front derailleurs). If your front derailleur included a stop plate and you're not installing it on a braze-on frame you definitely want this part!

This clamp on adapter has a small protrusion that interfaces directly with the support screw on Toggle Construction front derailleurs: