A penetrator is used to measure the hardness of a material. The Rockwell test system is based on the idea that the depth of penetration decreases as the hardness of the object being tested increases. The minor load is applied to the surface in order to condition it. The major load is applied and then released gradually. The minor load remains, but the difference between the depth of penetration before and after application of the major load is used to calculate the Rockwell hardness number. The specified penetrator was installed into the indenter fixture. A flat anvil or V-shaped anvil is installed to support the specimen.

The following penetrators are used in Standard Rockwell Hardness Test Blocks – ASTM E-18 and ISO 6508: C Diamond, A Diamond (Carbide), 1/16″ Ball, 1/8″ Ball, 1/4″ Ball and 1/2″ Ball.

Superficial Rockwell Hardness Test Blocks – ASTM E-18 and ISO 6508 use, on the other hand, such kinds of penetrators: N Diamond, 1/16″ Ball, 1/8″ Ball, 1/4″ Ball, 1/2″ Ball.