Advertise an electrical fitting (4)
I believe the answer is:
plug
'advertise' is the definition.
(I know that plug is a more specific form of the action advertise)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for plug that I've seen before include "quid" , "Piece of publicity" , "See 19" , "Wad, of tobacco say" , "Bung -- promotion" .)