An extruder is disclosed, and more particularly, a twin screw extruder for mixing, compounding, kneading and/or extruding of materials. The twin screw extruder includes a barrel assembly having a housing. The twin screw extruder further includes a first screw provided within the housing and comprising threads. The twin screw extruder further includes a second screw provided within the housing and comprising a threaded portion and a shaft portion devoid of threads. A drive system which drives the first screw and the second screw.