Find fault with round metal tool (3-4)

I believe the answer is:

nit-pick

'find fault with' is the definition.

'round metal tool' is the wordplay.
'round' shows that the letters should be reversed in order.
'metal' becomes 'tin' (tin is a kind of metal).
'tool' becomes 'pick' (pick is a kind of tool).
'tin' reversed gives 'nit'.
'nit'+'pick'='NIT-PICK'

I've seen this clue in The Guardian.

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