Does your press form an extruded meal slug? I've only seen the Komet (German) press thus far, and that is what they do. Their screws are not very long, maybe 8 inches, but are hard chromed and given an excellent finish. I've never tried to make a screw for this particular press, but I've heard of several attempts by others to make the screws, but apparently the Germans have some technical knowledge on chroming and finishing that escapes the imitators
Their presses are reportedly sometimes hard to 'prime' to get the meal to flow through if the screw is anything less than perfectly finished.
AFAIK, the head space restriction at the end of the barrel creates the pressure. Various gashes are present in the barrel and on the head to provide traction on the meal cake. The oil flow is essentially backwards through the meal through drip holes in the barrel.