SDDJ
A class: 40Cr
AA class: 20CrMnTi
A class Head hardness: 46-50HRC Hardness of the screw thread and other parts:35±5HRC
AA class Head hardness: 55-58HRC Hardness of the screw thread and other parts:35±5HRC
A class Accuracy: 0.02
AA class Accuracy: 0.01