Turning big red spanner (6)
I believe the answer is:
bridge
'spanner' is the definition.
(I've seen this before)
'turning big red' is the wordplay.
'turning' indicates anagramming the letters.
'big'+'red'='bigred'
'bigred' is an anagram of 'BRIDGE'.
(Other definitions for bridge that I've seen before include "Something of a nose" , "played by a quartet" , "Spanning structure to allow passage" , "Card game; structure" , "Structure carrying a road, railway etc." .)