Car wheel’s central disc (6)
![Ross](/clue/static/ross-mug.min.png)
I believe the answer is:
hubcap
(Other definitions for hubcap that I've seen before include "Wheel attachment" , "It fits over the centre of a wheel" , "It fits over the central part of a wheel" , "Protective plate for car wheel" , "Metal protector for car wheel" .)