Crossword Genius

Does it play an extra big part in car manufacture? (6)

Ross

I believe the answer is:

bumper

I'm a little stuck... Click here to teach me more about this clue!

'does it play an extra big' is the definition.
I can't tell whether this definition defines the answer.

'part in car manufacture?' is the wordplay.
'part' becomes 'bum' (bum is a kind of part).
'in car manufacture?' becomes 'per' (I can't justify this - if you can you should give a lot more credence to this answer).
'bum'+'per'='BUMPER'

Can you help me to learn more?

(Other definitions for bumper that I've seen before include "Something big" , "end on a car" , "Protective vehicle bar" , "jumbo" , "Glass filled to brim" .)

I've seen this clue in the Evening Standard.
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