Device for fastening loose plaster (7)
I believe the answer is:
stapler
'device' is the definition.
(stapler is a kind of device)
'loose plaster' is the wordplay.
'loose' indicates anagramming the letters (letters are loosened from their original positions).
'plaster' anagrammed gives 'STAPLER'.
'for fastening' acts as a link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for stapler that I've seen before include "Office equipment - plaster (anag)" , "Office fastener" , "Paper-fastening device" , "It's used to attach leaves" , "Implement for inserting paper fasteners" .)