Fastidiousness for exactness (6)
I believe the answer is:
nicety
I believe this clue is a double definition.
'fastidiousness' is the first definition.
(I've seen this before)
'exactness' is the second definition.
(thesaurus)
'for' acts as a link.
(Other definitions for nicety that I've seen before include "Fastidiousness" , "shade?" , "Delicacy" , "Refinement" , "Degree of precision" .)