Right or left, there may be no difference (4)

I believe the answer is:

sock

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'right' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Perhaps they are linked in a way I don't understand?

I don't understand the remainder of the clue.

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(Other definitions for sock that I've seen before include "One worn" , "impact" , "Foot garment" , "Very short stocking?" , "Garment; hard blow" .)

I've seen this clue in the Evening Standard.

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