Endeavour to get a wrench (6)
I believe the answer is:
strain
I believe this clue is a double definition.
'endeavour' is the first definition.
(strain is a kind of endeavour)
'a wrench' is the second definition.
(thesaurus)
'to get' acts as a link.
(Other definitions for strain that I've seen before include "Muscle injury, put liquid through sieve" , "line of ancestry" , "Sieve; breed" , "Strive; ancestry" , "Overwork - melody" .)