Principal pro desktop tool (6,3)

I believe the answer is:

staple gun

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

'desktop tool' is the definition.
I know nothing about this answer so I cannot tell whether this works.

'principal pro' is the wordplay.
'principal' becomes 'staple' (I've seen this before).
'pro' becomes 'gun' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'staple'+'gun'='STAPLE GUN'

Can you help me to learn more?

(Other definitions for staple gun that I've seen before include "Tool for inserting fasteners" , "One that fires those fixing" .)

I've seen this clue in the Sydney Morning Herald.

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.