A great big metal bar? (6)
I believe the answer is:
bumper
This could be a double definition.
'a great' is the first definition.
(thesaurus)
'big metal bar?' is the second definition.
'bumper' can be an answer for 'bar?' (I've seen this before). I am not sure about the 'big metal' bit.
Can you help me to learn more?
(Other definitions for bumper that I've seen before include "Unusually plentiful as a crop may be" , "Unusually large" , "Bar at either end of a vehicle" , "Protection for car" , "bouncer" .)