The Brinell Hardness of Graphite constant displays the value of the Brinell hardness for graphite (5 BHN).
Brinell hardness test determines the ability of a metal to resist permanent indentation deformation through the scale of penetration of an indenter that is loaded onto a material sample. Brinell hardness is one of several definitions of hardness for materials science.
The Brinell hardness of graphite is 5 Brinell hardness numbers (BHN).
Material Properties (https://material-properties.org/graphite-density-strength-hardness-melting-point/)