The AISI (American Iron and Steel Institute) was the originator of the 300 and 400 series numbering system (i.e. Type 304 stainless steel). They also published a stainless steel products manual that listed these designations and the typical chemical analysis and mechanical and physical properties of each individual grade. These documents were NOT specifications or material standards. The AISI has not issued numbers for stainless steel for some time. Although AISI numbers are still commonly used to generically identify stainless steels, the UNS (Unified Numbering System) numbering system is preferred internationally to identify specific chemistries. AISI or UNS numbers only indicate the chemistry, so it is important to also use to the appropriate material standards. In North America, the ASTM International standards should be used.