Essentially, all elements of the co-rotating twin screw extruder are an adaptation or variation of the basic "Erdmenger" geometry. The following basic dimensions can be varied here according to their interdependency:
OD/ID ratio
Outer diameter and inner diameter matched to the required OD/ID ratio
Flight pitch of the screw
Length of the element
Machine-specific clearances between the element and the barrel hole or the element and the adjacent element.
from: