Working part came to firm conclusion (8,3)

I believe the answer is:

business end

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'working part came' is the definition.
I can't tell whether this defines the answer.

'firm conclusion' is the wordplay.
'firm' becomes 'business' (synonyms).
'conclusion' becomes 'end' (something's conclusion is its end).
'business'+'end'='BUSINESS END'

'to' is the link.

Can you help me to learn more?

(Other definitions for business end that I've seen before include "That's the bit that works" , "part doing the work" , "Liquidation" , "Device's functional part" .)

I've seen this clue in the Sydney Morning Herald.

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