Fixer for boss establishes company (8)
I believe the answer is:
setscrew
'fixer for boss' is the definition.
(a setscrew might fix a boss or stud in place)
'establishes company' is the wordplay.
'establishes' becomes 'sets' (setting is a kind of establishing).
'company' becomes 'crew' (a group of people).
'sets'+'crew'='SETSCREW'
(Other definitions for setscrew that I've seen before include "means of exerting pressure" , "fastener that prevents movement" .)