Grease gun adapter

In a spring-loaded grease gun having a cylindrical barrel and a head cap assembly, said cylindrical barrel being sized to receive a grease cartridge and having first and second ends, said first end having an opening to receive a spring-loaded rod and the second end being threaded to receive said head cap assembly, the improvement comprising an adapter, said adapter having a cylindrical body and a threaded interior surface for mating with the threaded second end of said cylindrical barrel and an exterior surface having a plurality of rectangularly shaped protrusions, said head cap assembly having a pistol type dispenser appended to a cylindrical cup, said cylindrical cup having an interior surface sized to receive said cylindrical body of said adapter, said inner surface of said cylindrical cup comprising a plurality of cylindrical cup protrusions sized and positioned to mate with said rectangularly shaped protrusions emanating from the exterior surface of said adapter for frictionally joining said head cap assembly to said adapter.