1.18years experience for 38crmoala screw and barrel 2.alloy-steel 3.different ... 15mm~300mm2. Ratio of length to diameter:L/D=15~553.Tempering hardness:240~280HV4.Nitride hardness:900 ... . 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 etc ...