The SAE steel grades system is a standard alloy numbering system for steel grades maintained by SAE International. In the 1930s and 1940s the American Iron and Steel Institute (AISI) and SAE were both involved in efforts to standardize such a numbering system for steels. These efforts were similar and overlapped significantly. For several decades the systems were united into a joint system designated the AISI/SAE steel grades.
Source: Wikapedia “SAE Steel Grades”