The most commonly-used scales are “C” and “B”. The C scale is used for harder materials. It employs a diamond-cone indenter with a test force of 150 kgf, yielding hardness values denoted as “HRC”. The B scale applies to softer materials (such as aluminum, copper and mild steel). It uses a tungsten-alloy-ball indenter under a 100 kgf test force, producing hardness values expressed as “HRB”. Besides these, a variety of other scales are available for alternative applications.

Take “HBW 10/3000” as an example of the standard designation for Brinell hardness values: “HBW” indicates that a tungsten-alloy ball indenter is used (W is the chemical symbol for tungsten); “HBS” is used when a steel-ball indenter is adopted. “10” stands for the ball diameter in millimeters, and “3000” represents the test force in kilogram-force. Accuracy complies with GB/T 231.2, European and international standard EN ISO 6506, as well as American standard ASTM E10.

For all hardness - testing methods, the fundamental principle is to evaluate a material’s resistance to plastic deformation. The Vickers test is applicable to all metallic materials and enjoys the broadest range of applications in hardness measurement. Though both Knoop and Vickers hardness tests fall within micro - hardness testing, they differ in indentation geometry and measurement sensitivity. Knoop micro-hardness testers are generally preferred when testing thin coatings or brittle materials.