Shimano

XT, SLX Rear Derailleur Switch Lever Unit and Fixing Plate

Just wanted to pass along that this also fits GRX RD-RX810. It's Grey instead of Black--that's the only difference. The Grey actually allows you to see at a glance whether the clutch is On or Off. So don't go searching for Y3GE98030, just use Y5Y198010, which is easier to find--in fact, so easy to find that you might suspect Shimano did not make this part durable enough...