The screw should be single flighted,constant pitch,with the pitch equal to the diameter and the

length equal to 24 diameters.It should be bored for cooling.Screw Flights should be flamehardened.
The screw should be AISI4140 chrome plated.Since flexible PVC compounds can cover a wide range of

hardnesses,the screw design and dimensions are less critial than for rigid pvc.

Mixing pins and other types of mixing sections are often incorporated in a screw design to enhance dispersion,espeically when adding concentrates to a naturalbased compound.Screws with mixing

pins typically have 12-14 flights in the metering section.

Barrier screws are still another type of design that can be used for extruding flexible PVC.