Bits of pressure on things (9)

I believe the answer is:

particles

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'bits' is the definition.

'pressure on things' is the wordplay.
'pressure on' becomes 'p' (abbreviation. I am not sure about the 'on' bit.).
'things' becomes 'articles' (I've seen this before).
'p'+'articles'='PARTICLES'

'of' acts as a link.

Can you help me to learn more?

(Other definitions for particles that I've seen before include "Minute pieces of matter" , "Tiny pieces" , "Scraps" .)

I've seen this clue in The Mirror.

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