Abstract: Plasticating apparatus includes a barrel having an inlet for the introduction of resinous material and an outlet for the discharge of plasticated molten extrudate, along with a screw rotatably mounted within the barrel and in communication with the inlet and outlet for receiving resinous material, plasticating the resinous material, and discharging plasticated molten extrudate. The screw includes a helical flight with an outside diameter sized rotatably engaging an inside surface of the barrel and further, a helical valley disposed between flight lands of the helical flight within a transition section includes two root diameters, namely a rear root diameter and a forward root diameter, with the rear root diameter being larger than the forward root diameter proximate the inlet. In addition, a metering section is provided with special infeed and outfeed passages.