Hardness testing blocks are designed for metals hardness testers calibration.
There are available different standard nominal values of the blocks, such as: 25 HRC, 45 HRC, 65 HRC, 90 HRB, 83 HRA.
Basically, the blocks are made from Carbon Steel, but also available blocks are made from Brass and Aluminium.
The blocks meet ASTM E18 standard.