Firm support for some office equipment (6)
I believe the answer is:
copier
'some office equipment' is the definition.
(I've seen this before)
'firm support' is the wordplay.
'firm' becomes 'co' (a firm is a company).
'support' becomes 'pier' (pier is a kind of support).
'co'+'pier'='COPIER'
'for' acts as a link.
(Other definitions for copier that I've seen before include "Office item" , "Machine for making facsimiles" , "Machine for reproducing something" , "Something that duplicates" , "Machine for making duplicates" .)