Drilling tool used in putting fireguard back (5)
I believe the answer is:
auger
'drilling tool' is the definition.
(I've seen this in another clue)
'in putting fireguard back' is the wordplay.
'in' says the answer is hidden in the clue.
'back' shows that the letters should be reversed in order.
'regua' is hidden within 'putting fireguard'.
'regua' backwards is 'AUGER'.
'used' acts as a link.
(Other definitions for auger that I've seen before include "Tool for boring holes in wood" , "something that's boring" , "A drilling tool" , "Boring-tool" , "Boring instrument" .)