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) Purpose To measure the Rockwell hardness of brake linings. a. Rockwell hardness measures the depth of penetration. b. Gogan hardness measures the compression of the materials under load. (See SAE J379)