Diminutive fixer digs company (4,5)
I believe the answer is:
grub screw
'diminutive fixer' is the definition.
(type of small screw)
'digs company' is the wordplay.
'digs' becomes 'grubs' (both can mean to dig in soil).
'company' becomes 'crew' (I've seen this before).
'grubs'+'crew'='GRUB-SCREW'
(Other definitions for grub screw that I've seen before include "One secures" , "Fixer" , "Securing device" .)