The Rockwell test consists of measuring the additional depth to which a carbide ball or diamond penetrator is forced by a heavy (major) load beyond the depth of a previously applied light (minor) load (SET point).

The minor load is applied first and a SET position is established on the dial gauge or displacement sensor of the Rockwell tester. Then the major load is applied. Without moving the piece being tested, the major load is removed and, with the minor load still applied, the Rockwell hardness number is automatically indicated on the dial gauge or digital display.

The diamond penetrator is used for testing materials such as hardened steels and cemented carbides. The carbide ball penetrators, available with 1/16 inch, 1/8 inch, 1/4 inch, and 1/2 inch diameter, are used when testing materials such as steel-copper alloys, aluminum and plastics to name a few.

Rockwell testing falls into two categories: Regular Rockwell testing (e.g., C and B scales) and Rockwell superficial testing (e.g., 30 N and 30 T scales).

High Rockwell hardness numbers represent hard materials and low numbers soft materials.