One who won't admit stocking this fine unit? (6)
I believe the answer is:
denier
I believe this clue is a double definition.
'one who won't admit' is the first definition.
(someone who denies something)
'stocking this fine unit?' is the second definition.
(unit for measuring hosiery eg stockings)
(Other definitions for denier that I've seen before include "old coin" , "One who doesn't believe" , "One refusing to admit" , "One refuses to acknowledge" , "Unit of weight of nylon, etc" .)