... Nitrided Brittleness above 2 stage Surface Roughness ... 2.0mm Alloy hardness HRC56°~65° Alloy iron,nickel,tungsten,molybdenum Types of screw Gradual type,mutant type,wave type,barrier type,double screen type,shunt type,separation type ... ,exhaust type,pin type,mixed type,double-head type,three-head type,multi head type ...