Tool for working a spar (4)
I believe the answer is:
rasp
'tool' is the definition.
(rasp is a kind of tool)
'working a spar' is the wordplay.
'working' indicates an anagram.
'spar' with letters rearranged gives 'RASP'.
'for' is the link.
(Other definitions for rasp that I've seen before include "Abrade" , "Smoother" , "sort of berry?" , "Harsh grating sound" , "It is used to grate" .)