Zwift Hub / Wat is the black ring in the screw bag for?


I just received my brand new Zwift Hub with the 11-speed cassette. While assembling the Hub I noticed a black metal with an diameter of app. 4 cm which cam with the bag with the screws.

I could not found any description or note in the manual about this ring. Do you know what this ring is for? Has something fallen off my Hub during shipping?

Is it the spacer for a 10 speed cassette?

I also use it when using my seven speed hub with another larger spacerr