Annotation of standard text SAE J864 :
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.
SUBJECT TAXONOMY: Tools and equipment, Materials properties, Durability, Test procedures
SUBFILE: Automotive
TYPE OF DOCUMENT: Ground Vehicle Standard
Stabilized: Jan 2018 