This is the radiator cap screw that goes on the huge Adenauer grille.  Condition per photos, with the star missing from the circle.

I have a grille in my collection that has a different type of screw cap (I think a later version, where they tried to save money).  I screwed this on and it fit perfectly (see photos).

Genuine, vintage OEM, not a repro.

You are only getting the cap; there are a couple of photos of it mounted on an Adenauer grille but you are not getting the grille or the badge, just the radiator cap shown in the rest of the photos.