The UNS provides a method for correlating the metal and alloy numbering systems developed by various technical associations. It has been developed to avoid designating more than one number for the same metal or alloy and to avoid designating the same number for different metals or alloys, and it has been in use since 1974. Currently, there are 5,200 designations for metals and alloys. It should be noted that a UNS designation is not a specification because it does not establish requirements for properties such as mechanical properties and heat treatment.

The UNS designates 18 series to identify metals and alloys. Each UNS designation consists of a single letter followed by five digits. To the greatest extent possible, commercially popular numbers are incorporated in the UNS system. For example, the UNS designation for AISI 1018 is G10180.