PIN number 1150? (4)

I believe the answer is:

nail

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

'pin' is the definition.
(I've seen this before)

'number 1150?' is the wordplay.
'number' becomes 'n' (n can represent any number).
'aa50?' becomes 'ail' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'n'+'ail'='NAIL'

Can you help me to learn more?

(Other definitions for nail that I've seen before include "Claw" , "Metal spike with head" , "Amall metal spike" , "Fasten, catch (criminal)" , "Brad or tack" .)

I've seen this clue in The Guardian.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.