Turning, it applies pressure round the ring (5)
I believe the answer is:
rotor
'ring' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Perhaps you can see an association between them that I can't see?
I can't explain the rest 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" .)