The AISI (American Iron and Steel Institue) was the originator of the 300 and 400 series numbering system(i.e. Type 304 stainless steel) They  also published a stainelss steel products manual that listed these designations and thetypical 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 mumber only indicate the chmistry, so it is important to also use to the appropriate material standards. In North America, the ASTM Internationl standards should be used.