Tubular form of hat? (5)

I believe the answer is:

straw

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'hat?' is the definition.
(I've seen this in another clue)

I cannot understand how the rest of the clue works.

(Other definitions for straw that I've seen before include "It's clutched at in desperation" , "What a sucker gets given" , "Stems left after grain has been removed" , "In the wind, it's an indication" , "corny stuff" .)

I've seen this clue in the Evening Standard.

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