Model metropolitan headgear (6)
I believe the answer is:
turban
'headgear' is the definition.
(I know that turban is a type of cap)
'model metropolitan' is the wordplay.
'model' becomes 'T' (Ford Model T car).
'metropolitan' becomes 'urban' (I've seen this in another clue).
't'+'urban'='TURBAN'
(Other definitions for turban that I've seen before include "Wound headgear" , "Headdress worn by Sikh men" , "Religious head covering" , "it provides cover for head" , "Cloth wound around the head" .)