Margaret briefly referred to fixture for hanging (3)
I believe the answer is:
peg
This clue is a double definition.
'margaret briefly referred to' is the first definition.
(nickname for someone called Margaret)
'fixture for hanging' is the second definition.
(a peg is for hanging things on)
(Other definitions for peg that I've seen before include "This leg is artificial" , "Brandy and soda drink measure" , "Wooden or plastic pin for hanging clothes" , "that may have hat or coat on" , "Old song: ''... o' my heart''" .)