Kilos, for example, in cask (3)
I believe the answer is:
keg
'cask' is the definition.
(I know that keg is a type of cask)
'kilos for example' is the wordplay.
'kilos' becomes 'k' (abbreviation).
'for example' becomes 'eg' (short for 'exempli gratia', 'for example' in Latin).
'k'+'eg'='KEG'
'in' is the link.
(Other definitions for keg that I've seen before include "Small beer cask" , "Barrel as for beer" , "Small cask or barrel" , "Sort of beer" , "What's found at King's Head" .)