Area of Northumberland that's handy for suckers? (5)

I believe the answer is:

thumb

I'm a little stuck... Click here to teach me more about this clue!

'area of northumberland that's handy for suckers?' is the definition.
I can't judge whether this defines the answer.

'area of northumberland that's' is the wordplay.
'area of' indicates a hidden word (I've seen this in other clues).
'THUMB' is hidden in the letters of 'northumberland that'.

Can you help me to learn more?

(Other definitions for thumb that I've seen before include "Second part of 12" , "Tom's digital fairy tale" , "Hitch-hiking digit" , "''Tom ..., the piper's son'' (nursery rhyme)" , "Hitchhike - ..... a lift" .)

I've seen this clue in The Guardian.

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