Restraints for links (4)
I believe the answer is:
ties
I believe this is a double definition.
'restraints' is the first definition.
(I know this)
'links' is the second definition.
(tie can mean a connection or link)
'for' acts as a link.
(Other definitions for ties that I've seen before include "Links" , "Attaches, knots" , "Fastens with a knot" , "allegiances" , "Items of neckwear" .)