What are the different scales used to represent Rockwell hardness testers?

Taiwan Nakazawa answers you.
HRA: Hardness obtained by using a 60kg load and a diamond cone indenter, used for materials with extremely high hardness (such as tungsten carbide, hard alloys, etc.).
HRB: Hardness obtained by using a 100kg load and a hardened steel ball with a diameter of 1.5875mm, used for materials with lower hardness (such as annealed steel, cast iron, etc.).
HRC: Hardness obtained by using a 150kg load and a diamond cone indenter, used for materials with very high hardness (such as quenched steel, etc.).