I believe there is no corelation between the grade of the bond and machanical scales like Rockwell and Knoop. The grade of the wheel reflects how strong the bond holds abrasive grains and not how hard a material it is. Two methods are used to test the grade of the vitrified bond wiht CBN: sandblasting and sound conductvity. In first case, a spot on the wheel is sandblasted and the cavity is measured. The softer the bond, the larger the cavity. In second case, special electronic device measures the sound conductivity of the wheel. For more info write me at gurinovich@abrazive.spb.ru