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January/February 2009

The Unified Numbering

The Unified Numbering System catalogs metals and alloys, and it provides an international identification system that is clear, understandable and useful.

Developed and published jointly by SAE International and ASTM International, Metals and Alloys in the Unified Numbering System has been in use since 1974. Now in its 11th edition, published last year, the UNS contains more than 5,000 designations, up more than 125 since the 10th edition in 2004, and the work’s Index of common trade names has more than 4,500 additions.

Not a specification, because it establishes no material requirements, a UNS designation labels a metal or alloy that has controlling limits established in specifications published elsewhere. Rather, the UNS establishes 18 series of designations for metals and alloys with a single-letter prefix followed by five digits. The letter typically suggests the family of metals identified: A for aluminum, C for copper, N for nickel and S for stainless steel, for example.

The UNS includes metals and alloys designations from such technical societies and specifying organizations as the Aluminum Association, the American Society of Mechanical Engineers, the American Welding Society, ASTM International, the Copper Development Assocation, the International Organization for Standardization, NACE International and SAE International.

The work is overseen by a volunteer group of experienced, highly qualified metallurgists responsible for each of the series of metals and alloys. More details about the standard used to assign the numbers can be found in ASTM E527, Practice for Numbering Metals and Alloys in the Unified Numbering System, which is included as part of the UNS reference.

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