Bird pen fixture with round ridge opening tipped over (5)

I believe the answer is:

robin

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'bird' is the definition.
(robin is a kind of bird)

I don't understand the rest of the clue.

(Other definitions for robin that I've seen before include "Small brown and red bird" , "Red-breasted Christmas card bird" , "Bird on many cards" , "Bird; man's name" , "Seasonal bird" .)

I've seen this clue in The Guardian.

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