Spots on reading glasses (6)

I believe the answer is:

specks

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'spots' is the definition.
(I know this)

'on reading glasses' is the wordplay.
'on' is an insertion indicator (as in clothing 'on' a person).
'reading' becomes 'k' (I can't justify this - if you can you should believe this answer much more).
'glasses' becomes 'specs' (spectacles).
'k' going into 'specs' is 'SPECKS'.

Can you help me to learn more?

(Other definitions for specks that I've seen before include "Tiny pieces as of dust" , "Tiny spots" , "What may help one to see" , "Small pieces as of dust" , "tiny things" .)

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

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