Turning, it applies pressure round the ring (5)

I believe the answer is:

rotor

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

I don't understand the remainder of the clue.

Can you help me to learn more?

(Other definitions for rotor that I've seen before include "Dynamo part" , "Bit of chopper" , "Revolving part of machinery" , "It lifts helicopter" , "Revolving bar" .)

I've seen this clue in the Evening Standard.

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