Hardness measurements are used as a quality control check of the consistency of formulation and processing of brake linings. This hardness method is nondestructive. NOTE This method is not a measure of friction level. The hardness and the range of hardness are characteristic of each formulation; therefore, the acceptable values and ranges must be established for each formulation and may be affected by processing. NOTE The hardness of sintered powder metal lining is usually determined with Rockwell superficial hardness equipment. (See ASTM B 347)