The measure of hardness for tool steels is most commonly done with a Rockwell tester. (See Rockwell.) The best hardness for a given steel is not necessarily the best for another. Generally, steel blades should be hardened to the high 50s or low 60s on the Rockwell C scale. An exception to general hardness rule: Stelite (not a steel) will be about 42 on the Rockwell C scale.