The Unified Numbering System (UNS) is an alloy designation system widely accepted in North America. It consists of a prefix letter and five digits. A prefix of S indicates steel alloys, C for copper, brass, or bronze alloys, T for tool steels, etc. The first three digits often match older three-digit numberins systems, while the last two digits indicate more modern variations. For example, Copper Alloy No. 377 (forging brass) in the original three-digit system became C37700 in the UNS System. The UNS is managed jointly by the American Society for Testing and Materials and the Society of Automotive Engineers.

Some common materials and translations to other standards:

• UNS S17400 is ASTM grade 630, Cr-Ni 17-4PH
• UNS S30400 is AISI 304, Cr/Ni 18/8, Euronorm 1.4301
• UNS C95400 is Ampco 18 aluminum bronze

alloys