For metric fasteners, I recommend ISO 898-1 Mechanical properties of fasteners. In addition to the material it contains, it refers to the specifications that cover the actual hardness tests - ISO 6506 (Brinell), ISO 6507-1 (Vickers), ISO 6507-2 (micro Vickers), and ISO 6508 (Rockwell). Equivalent ASTM specifications are F606M (fasteners), E10 (Brinell), E92 (Vickers), E384 (micro), and E18 (Rockwell).