Pens produced by Old Bob, for example, with a carbon twist (5)
I believe the answer is:
cages
'pens' is the definition.
(both can mean locks up or imprisons)
'old bob for example with a carbon twist' is the wordplay.
'old bob' becomes 's' (abbreviation for bob or shilling used before e97e).
'for example' becomes 'eg' (short for 'exempli gratia', 'for example' in Latin).
'with' means one lot of letters go next to another.
'carbon' becomes 'C' (chemical symbol).
'twist' says the letters should be written backwards (I've seen 'twisting' mean this (letters twist back)).
's'+'eg'+'a'+'c'='segac'
'segac' written backwards gives 'CAGES'.
'produced by' acts as a link.
(Other definitions for cages that I've seen before include "prisons" , "Locks up" , "Enclosures made or wire or metal bars" , "Enclosures for animals" , "Wild animal enclosures" .)