Film company couples - they're all-round swingers (9,6)

I believe the answer is:

universal joints

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'film company couples' is the definition.
Although both the answer and 'film' are nouns, they are not in the same form of the noun.

'all-round swingers' is the wordplay.
'all round' becomes 'universal' (universal means widespread).
'swingers' becomes 'joints' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'universal'+'joints'='UNIVERSAL JOINTS'

'they're' is the link.

Can you help me to learn more?

I've seen this clue in The Independent.

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