The set includes two turned brass barrels with drilled cooling jacket.
Used on most Italian aircraft during World War II (Fiat CR.42, Fiat G.50, Macchi MC.200, Macchi MC.202, Reggiane Re.2000 etc.)
It is very simple to use in Your model, and makes it extremely realistic. Insert the metal parts using Cyanoacrylate adhesives. Drill proper hole in plastic part if needed.