Wrench, for one (4)
I believe the answer is:
tool
'wrench for one' is the definition.
(I know that spanner is a type of hand tool)
This is all the clue.
(Other definitions for tool that I've seen before include "Hand implement" , "one of 12 [SPADES] , for example" , "Utensil; implement" , "Person exploited" , "Maybe saw" .)