Union member carrying good spanner (6)
I believe the answer is:
bridge
'spanner' is the definition.
(I've seen this before)
'union member carrying good' is the wordplay.
'union member' becomes 'bride' (I've seen this in other clues).
'carrying' is an insertion indicator.
'good' becomes 'g' (abbreviation).
'bride' going around 'g' is 'BRIDGE'.
(Other definitions for bridge that I've seen before include "Join" , "Connection crossing river etc" , "Card game - pontoon - couple" , "Something of a nose" , "Span of popular card game" .)