Rod's joint, perhaps? (7)

I believe the answer is:

ferrule

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'rod's' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Maybe there's an association between them I don't understand?

I cannot understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for ferrule that I've seen before include "Protective metal cap" , "Metal band on the tip of a stick" , "Cap for protecting the tip of a walking-stick" , "Metal cap on end of stick" , "Metal band on umbrella" .)

I've seen this clue in the Evening Standard.

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