The screw mechanism they describe is quite a bit different than an injection molding screw. The screw in an injection molder is like an auger, designed to push plastic pellets. A hobbed bolt is not an option because it can't pick up the pellets. Here they are grabbing the filament from the outside with threads, kind of like rifling.

Reading the paper, it seems like they managed to double the force compared to a traditional pinchwheel. However, there are now extruders that used geared pinchwheels on both sides of the filament, doubling the force without requiring threading the filament.