Steel ring (4)
I believe the answer is:
gird
I believe this clue is a double definition.
'steel' is the first definition.
(I've seen this before)
'ring' is the second definition.
(girding is a kind of ringing)
(Other definitions for gird that I've seen before include "Encircle - fasten with belt" , "Put a belt on" , "ring" , "Surround" , "Steel" .)