Run off to get fastener (4)
I believe the answer is:
bolt
This clue is a double definition.
'run off' is the first definition.
('bolt' can be a synonym of 'run off')
'fastener' is the second definition.
(bolt is a kind of fastener)
'to get' is the link.
(Other definitions for bolt that I've seen before include "Rush away - fastening bar" , "Leg it < and consume apace" , "Sprint? Yes he does!" , "It makes fast" , "Find a bar" .)