One sticking to the drill? (3)

I believe the answer is:

bur

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'drill?' is the definition.
(small surgical drill)

I cannot understand how the remainder of the clue works.

(Other definitions for bur that I've seen before include "Clinging seed case" , "Prickly seed case" , "sticker" , "small drill" , "Seed-case" .)

I've seen this clue in the Evening Standard.

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