1. Diameter: The diameter of the parallel twin screw is the same, and the diameter of the small end of the tapered twin screw is different from the diameter of the large end.
2. Concentric distance: The center distance of the flat twin screw is the same, the two axes of the conical twin screw are at an angle, and the size of the center distance varies along the axis.
3. Length to diameter ratio: Parallel double screw (L/D) refers to the ratio of the effective part length of the screw to the outer circle of the screw. The conical twin screw (L/D) refers to the effective part length and the large end diameter and small of the screw. The ratio of the average of the end diameters.