Kilos, for example, in cask (3)
I believe the answer is:
'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).
'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" .)