A humble, down-to-earth turner (4)

I believe the answer is:

worm

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

This is the entire clue.

Can you help me to learn more?

(Other definitions for worm that I've seen before include "Wriggly creature" , "Squirm" , "Wriggle" , "Screw thread; maggot" , "one leaving cast" .)

I've seen this clue in the Evening Standard.

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