Faucet handle adapter part

Don't know if this is a generic part or specific to this faucet handle model, at least it has worked for me.

Edit: User [Arne S](https://www.printables.com/social/262134-arne-s/about) [over at printables](https://www.printables.com/model/115052-faucet-handle-adapter-part/comments) tells me the correct German term is "Rastbuchse"