That nut in Company B (3)
I believe the answer is:
cob
'that nut' is the definition.
(cob is a kind of nut)
'company b' is the wordplay.
'company' becomes 'co' (abbreviation).
'co'+'b'='COB'
'in' acts as a link.
(Other definitions for cob that I've seen before include "Horse, male swan and loaf of bread" , "Round loaf of bread" , "mount" , "Swan of Jacobean origin" , "Hazelnut" .)