... the double alloys:HRC56-656)Fully hard screw(wear-proof, corrosion-proof, heatproof, high-pressure proof and high-speed proof):HPT1 HPT2 HPT37)depth of ... double alloys:HRC56-65 6)Fully hard screw(wear-proof, corrosion-proof, heatproof, high-pressure proof and high-speed proof):HPT1 HPT2 HPT3 7)depth ...