Brinell Hardness
In the Brinell test (generally used for metals of uniform hardness), a hard object such as a steel ball is pressed into the material being tested. The ball is of a specified diameter, usually 1 centimeter. The Brinell hardness is the amount of force applied to the ball divided by the area of the indentation the ball makes in the material. The result is measured in kilograms of force per square millimeter but should be stated as an empirical reading, without units.

Rockwell Hardness
In a Rockwell hardness test, a penetrator makes an indentation in the metal under two constant loads, a "minor" load (generally 10 kilograms) and then a "major" load. The difference in penetration depth between the two loads provides the measure of the hardness, usually read from a gauge on the testing machine. There are several Rockwell scales for different ranges of hardness. The most common are the B scale (RHB), for which a steel ball is used as the penetrator, and the C scale (RHC), for which a cone-shaped diamond is used. The B scale is appropriate for soft metals, the C scale for hard metals. Rockwell hardness numbers are not proportional to Brinell hardness readings.

Tensile Strength
The quantity of stress needed to overcome a material resistance to structural failure.