Think it proper to check the size and shape (3,3)
I believe the answer is:
see fit
'think it' is the definition.
I can't tell whether this definition defines the answer.
'proper to check the size and shape' is the wordplay.
I cannot really see how this works, but
'proper' could be 'fit' (I've seen this in another clue) and 'fit' is found in the answer.
'check' could be 'see' (synonyms) and 'see' is found in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for see fit that I've seen before include "Consider to be proper or desirable" , "Consider appropriate or choose to do" , "Perceive in good shape, so choose to do?" , "Think suitable" , "Want" .)