... L/D: 30/1 Material of screw: 38CrMoAl Surface treatment: nitriding processing, thickness: 0.6 ~ 0,8mm, Polishing Max. rotating speed ... Material of screw: 38CrMoAlA. Max. rotating speed: 8rpm Surface treatment: nitriding processing, thickness: 0.6 ~ 0,8mm, Polishing♦ Two chambers vacuum ...