The Rockwell Hardness Test presses a steel or diamond hemisphere-conical penetrator against a test specimen and measures the resulting indentation depth as a gage of the specimen hardness. The harder the material, the higher the HR reading.

In the test, a minor load (10 kgf) is first applied, and the test dial (measuring the indention depth) is reset to zero. Then a major load (60, 100, or 150 kgf) is applied to create the full indention. The major load is reduced back to the minor load, and the indention depth measurement is taken.

The penetrator is usually 1/16 inch in diameter, although larger diameters (such as 1/8 inch) may be used for softer metals. Choosing the proper penetrator and the corresponding load requires experience. Some commonly used combinations are summarized below:

Scale	Condition	Application
A	Brale indenter 60 kgf load	Thin, hard sheet materials, such as tungsten carbide.
B	1/16 in diamond ball 100 kgf load	Medium/low hard materials, such as annealed carbon steels.
C	Brale indenter 150 kgf load	Materials harder than HRB 100.
D	Brale indenter 100 kgf load	Case-hardened materials.
F	1/16 inch Brale indenter 60 kgf load	Soft materials, such as bearing metals.
N	1/16 inch Superficial Brale indenter 15, 30, or 45 kgf load	Unhardened materials, such as metals softer than hardened steel or hard alloys, or where shallow indentations are desired.
T	1/16 inch diamond ball 15, 30, or 45 kgf load	Unhardened materials, such as metals softer than hardened steel, or where shallow indentations are desired.