This is the Lock Ring and O-ring kit to hold the front chainring and/or spider onto the motor drive pinion on the Bosch Gen 4 Drive Unit (BDU4XX)
Substantially tougher than the plastic nuts, although be careful not to cross thread the nut on the drive unit assembly.
PLEASE NOTE: If you have a Bosch Classic +, Active Plus or Performance system (Featuring a small sprocket on the front), you will require a different lockring.
We also sell the Bosch Spider Tool to safely remove and replace this nut. (See related products tab).
Just to confirm it's to fit the following motor shape. If you require a Classic+ lock ring, you can find it here.