Abstract: A mixing section for an extrusion or injection screw has alternating helical wiping and barrier lands which form inlet and outlet channels therebetween, with the barrier lands having a greater helix angle than the wiping lands, creating a conjunction of the adjoining wiping and barrier lands near the input and exit ends of the mixing section. The barrier lands also have notches cut therefrom to promote mixing and throughput. The barrier lands are widened at the conjunction with the wiping lands to form the termination of the downstream end of the inlet channels and the beginning of the upstream end of the outlet channels. Some or all of the channels do not have uniform depths such that the channels gently rise up to the narrowed beginning of the outlet channels and the narrowed ending of the inlet channels, with this tapering avoiding any pocket or hang-up area where melt flow could gather or degrade.