A first and common device used in industry to test pellet hardness is the ‘Kahl’
device (Fig. 3), analogous to the early developed, manually used Stokes tester. In the
Kahl device, a pellet is inserted between two bars, and by increasing statical pressure
applied by means of a spring, the force needed to crack the pellet is determined. The
average of ten measurements is referred to as the ‘Kahl-hardness’ of the pellet.