Does it make a clean contact for a nut? (6)

I believe the answer is:

washer

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'nut?' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Perhaps you can see an association between them that I don't see?

I don't understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for washer that I've seen before include "Joint-sealing ring" , "Plumber often wants it" , "Rubber ring securing joint" , "Laundress" , "Metal ring - cleans clothes" .)

I've seen this clue in the Evening Standard.

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