Fasten screen behind unframed grid (5)
I believe the answer is:
rivet
'fasten' is the definition.
(I know that rivet is a more specific form of the action fasten)
'screen behind unframed grid' is the wordplay.
'screen' becomes 'vet' (screen can mean to check or vet).
'behind' is a charade indicator (letters next to each other).
'unframed grid' becomes 'ri' (I can't justify this - if you can you should believe this answer much more).
'vet' put after 'ri' is 'RIVET'.
Can you help me to learn more?
(Other definitions for rivet that I've seen before include "Short metal fastener" , "make fast" , "Fascinate" , "Metal bolt that's hammered" , "Completely engross; pin" .)