Feb 24, 2016 · Hot Feed Extruder: Cold Feed Extruder: L/D ratio varies from 4: 1 to 5: 1. In many cases the screw has increasing pitch. L/D ratio varies from 15: 1 to 20:1. The screw has decreasing pitch. The screw has increasing root dia with more flight depth at feed end which increase from feed to discharge.