Metal guide (4)
I believe the answer is:
lead
This clue is a double definition.
'metal' is the first definition.
(I know that lead is a type of metal)
'guide' is the second definition.
(lead can mean to usher or guide)
(Other definitions for lead that I've seen before include "Short wire used as jumper - Pb" , "first guitarist" , "Be in charge of, element" , "Travel in front of" , "Metal; show the way" .)