The Unified Numbering System for Metals and Alloys (UNS) provides a means of correlating many internationally used metal and alloy numbering systems currently administered by technical societies, trade associations, and those individual users and producers of metals and alloys. This system avoids the confusion caused by the use of more than one identification number for the same metal or alloy, and the opposite situation of having the same number assigned to two or more different metals or alloys.

It provides the uniformity necessary for efficient indexing, record keeping, data storage and retrieval, and cross-referencing.

A UNS designation is not, in itself, a specification, because it establishes no requirements for form, condition, property, or quality. It is a unified identifier of a metal or an alloy for which controlling limits have been established in specifications published elsewhere.

The UNS establishes 18 series of designations for metals and alloys. Each UNS designation consists of a single-letter prefix followed by five digits. In most cases, the letter is suggestive of the family of metals identified: for example, A for aluminum, P for precious metals, S for stainless steels.

Although some of the digits in certain UNS designation groups have special assigned meanings, each series of UNS designations is independent of the others in regard to the significance of digits. This permits greater flexibility and avoids complicated and lengthy UNS designations.

Wherever feasible, and for the convenience of the user, identification “numbers” from existing systems are incorporated into the UNS designations. For example, carbon steel presently identified by the American Iron and Steel Institute as “AISI 1020” is covered by the UNS designation “G10200.”

The UNS designation assignments for certain metals and alloys are established by the relevant trade associations which, in the past, have administered their own numbering systems; for other metals and alloys, UNS designation assignments are administered by SAE International. Each of these assigners has the responsibility for administering a specific UNS series of designations. Each considers requests for the assignment of new UNS designations, and informs the applicants of the action taken. UNS designation assigners report immediately to the office of the Unified Numbering System for Metals and Alloys the details of each new assignment for inclusion into the system.

For additional details on the UNS System, see J1086 OCT2012, “Numbering Metals and Alloys,” and ASTM E527-16, “Standard Practice for Numbering Metals and Alloys in the Unified Numbering System (UNS),” included in Appendix B.

The listed cross-referenced specifications are representative only and are not necessarily a complete list of specifications applicable to a particular UNS designation.

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