The Unified Numbering System (UNS) is the accepted alloy designation system in North America for wrought and cast copper and copper alloy products.

The three-digit system developed by the U.S. copper and brass industry was expanded to five digits following the prefix letter C and made part of the Unified Numbering System for Metals and Alloys. UNS designations are simply expansions of the former designations.
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. Because these old numbers are embedded in the new UNS numbers, no confusion need result.  This designation system is also used in Canada.

The designation system is an orderly method of defining and identifying coppers and copper alloys; it is not a specification. It eliminates the limitations and conflicts of alloy designations previously used and at the same time provides a workable method for the identification marking of mill and foundry products.

The designation system is administered by the Copper Development Association Inc. New designations are assigned as new coppers and copper alloys come into commercial use, and designations are discontinued when an alloy composition ceases to be used commercially. Anyone may request changes in the list.

New designations are assigned if a copper or copper alloy meets three criteria:

1. The complete chemical composition is disclosed.
   
2. The copper or copper alloy is in commercial use or is proposed for commercial use.
   
3. The composition does not fall within the limits of any designated composition already in the list.
   

In the designation system, numbers from C10000 through C79999 denote wrought alloys. Cast alloys are numbered from C80000 through C99999. Within these two categories, the compositions are grouped into the following families of coppers and copper alloys: