Polish term (edited): twardo�� kulkowa

"Ball Hardness

A polished hardened steel ball with a diameter of 5 mm is pressed into the surface of a test specimen (at least 4 mm thick) with a force of 358 Newton (ISO 2039-1). After 30 seconds of load application, the depth of the impression is measured, from which the surface area of the impression is calculated. Ball hardness H358/30 is calculated as applied load divided by surface area of impression. Results are reported in Newtons per mm2."
http://www.engineeringreference.com/Properties/hardness prop...