Hardness testing with files consists essentially of cutting or abrading the surface of metal parts@ and approximating the hardness by the feel@ or extent to which@ the file bites into the surface. The term file hard means that the surface hardness of the parts tested is such that a new file of proven hardness will not cut the surface of the material being tested.
SAE J864-1963 history
2018SAE J864-2018 Surface Hardness Testing with Files
1993SAE J864-1993 Surface Hardness Testing with Files
1988SAE J864-1988 SURFACE HARDNESS TESTING WITH FILES
1984SAE J864-1984 Surface Hardness Testing with Files@ Recommended Practice
1963SAE J864-1963 SURFACE HARDNESS TESTING WITH FILES