In metals, ceramics and most polymers the deformation considered is plastic deformation of the surface.

Hardness measurements are widely used for the quality control of materials because they are quick and considered to be nondestructive tests, when the marks or indentations produced by the test are in low stress areas.

Brinell test was invented by Dr. J. A. Brinell in Sweden in 1900. The Brinell hardness system is one of the most widely used systems for indicating the hardness of metals and alloys. Brinell test uses a desktop machine for applying on a specified load to a hardened sphere of a specified diameter. Brinell hardness number can be represented by HB.

The Rockwell Hardness test was invented by Stanley P. Rockwell. The Rockwell Hardness test also uses a machine to apply a specific load and then measure the depth of the resulting impression. Rockwell hardness number can be represented by HRB.

When the material is very thin, lighter loads must be used, resulting in Rockwell 30T. The test measures the hardness by pressing an indentor into the surface of the steel with a specific load and them measuring how far the indentor was able to penetrate.

HR15T can be represented as Rockwell Superficial 15-T Scale. The Rockwell Superficial Hardness Tester is used to test thin materials, lightly carburized steel surfaces or parts that might bend or crush under the conditions of the regular test. This tester uses the same indenters as the standard Rockwell tester but the loads are reduced.