New worry, finding fastener (4)
I believe the answer is:
nail
'fastener' is the definition.
(I know that nail is a type of fastener)
'new worry' is the wordplay.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'worry' becomes 'ail' (I've seen this before).
'n'+'ail'='NAIL'
'finding' acts as a link.
(Other definitions for nail that I've seen before include "it needs hammering home" , "Bring down" , "Metal spike with head" , "Amall metal spike" , "Brad, for example" .)