The Unified Numbering System for Metals and Alloys (UNS) provides means of correlating many internationally used metal and alloy numbering systems currently administered by 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.

CA 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 9 series of designations for ferrous 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, F for cast irons, T for tool steel, 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, thus permitting greater flexibility and avoiding 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 the Society of Automotive Engineers (SAE). 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.

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

D00001-D99999	Steels with specified mechanical properties
D40450-D40900	Carbon Steels
D50400-D52101	Alloy Steels Casting
F00001-F99999	Cast irons
F 10001-F15501	Cast Iron, Gray
F 10090-F10920	Cast Iron Welding Filler Metal
F 20000-F22400	Cast Iron, Malleable
F 22830-F26230	Cast Iron, Pearlitic Malleable
F 30000-F36200	Cast Iron, Ductile (Nodular)
F 41000-F41007	Cast Iron, Gray, Austenitic
F 43000- F43030	Cast Iron, Ductile (Nodular), Austenitic
F45000 F 45009	Cast Iron, White
F47001-F47006	Cast Iron, Corrosion
G00001-G99999	AISI and SAE carbon and alloy steels (except tool steels)
G10050-G10950	Carbon Steel
G15130-G15900	Carbon Steel
G11080-G11510	Resulfurized Carbon Steel
G12110-G12150	Rephosphorized and Resulfurized Carbon Steel
G13300-G13450	Mn Alloy Steel
G40120-G48200	Mo Alloy Steel, Cr-Mo Alloy Steel, Ni-Cr-Mo Alloy Steel, Ni-Mo Alloy Steel
G81150-G88220	Ni-Cr-Mo Alloy Steel
G50150-G52986	Cr Alloy Steel, Cr-B Alloy Steel
G61180-G61500	Cr-V Alloy Steel
G92540-G98500	Cr-Si Alloy Steel, Si-Mn Alloy Steel, Cr-S-Mn Alloy Steel, Ni-Cr-Mo Alloy Steel, Ni-Cr-Mo-B Alloy Steel
H00001-H99999	AISI and SAE H-steels
H10380-H15621	H-Carbon Steel, C-Mn H-Alloy Steel, C-B H Carbon Steel, Mn H-Carbon Steel, B- Mn H -Carbon Steel
H40270-H48200	C-Mo H-Alloy Steel, Cr-Mo H-Alloy Steel Ni-Mo H-Alloy Steel
H50401-H51601	C-Cr-B H-Alloy Steel, C-Cr H-Alloy Steel
H61180-H61500	Cr-V H-Alloy Steel
H81451-H94301	Ni-Cr-Mo H-Alloy Steel
J00001-J99999	Cast steels (except tool steels)
J01700-J05003	Carbon Steel Casting
J11442-J84090	Alloy Steel Casting
J91100-J92001	Austenitic Manganese Steel Casting, Alloy Steel Casting
J92110-J93000	Alloy Steel Casting Precipitation Hardening, Alloy Steel Casting, Cast Cr-Ni-Mo Stainless Steel, Cast Cr-Ni Stainless Steel, Cast Cr-Mn-Ni-Si-N Stainless Steel
J93001-J95705	Stainless Steel Casting, Cast Cr-Ni-Mo Stainless Steel, Alloy Steel Casting, Maraging Cast Ferritic-Austenic Stainless Steel, Duplex Alloy Steel Casting, Alloy Steel Casting
K00001-K99999	Miscellaneous steels and ferrous alloys
K00040-K08500	Carbon Steel, Carbon Steel with Special Magnetic Properties, Steel Welding Rod, Enameling Steel
K10614-K52440	Alloy Steel, Alloy Steel Electrode and Welding Wire, High-Strength Low-Alloy Steel
K90901-K95000	Alloy Steel, Superstrength; Ferritic Cr-Mo-V Steel; Manganese Steel, Nonmagnetic; Ni-Co Steel Welding Wire; Iron, Electrical Heating Element Alloy; Iron Thermostat Alloy; Martensitic Age-Hardenable Alloy; Maraging Alloy; Fe-Co Soft Magnetic Alloy; Nickel Steel; Invar; Iron, Nickel Sealing Alloy; etc.
S00001-S99999	Heat and corrosion resistant steels (stainless), valve steels, iron-base "super alloys"
S13800-S17780	Precipitation Hardenable Cr-Ni-Al-Mo-(Cu, Ti) Stainless Steels
S20100-S39000	Austenitic Cr-Mn-Ni (Si,Mo,Cu,Al) Stainless Steel; Thermal Spray Wire; Austenitic Cr-Mn-Ni Stainless Steel and Welding Filler Metal; Austenitic Cr-Ni Heat Resisting Steel and Welding Filler Metal; Precipitation Hardenable Cr-Ni-(Si, Ti, Mo, Al) Stainless Steel, etc.
S40300-S46800	Martensitic Cr Stainless Steel; Ferritic Cr Stainless Steel with Ti or Ni or Mo; Martensitic Cr-Ni-Mo Stainless Steel; Hardenable Cr Stainless Steel
S50100-S50500	Cr Heat Resisting Steels and Filler Metal
S63005-S64007	Valve Steel
S65006-S65007	Valve Steel
S65150-S67956	Iron Base Super alloy
T00001-T99999	Tool steels, wrought and cast
T11301-T12015	High-Speed Tool Steels
T20810-T20843	Hot-Work Tool Steels
T30102-T 30407	Cold Work Tool Steels
T31501-S31507	Oil-Hardening Steels
T41901-T41907	Shock-Resisting Tool Steels
T51602-T51621	Mold Steels
T60601-T60602	C-W Tool Steels
T61202-T61206	Low-Alloy Tool Steels
T72301-T72305	Water Hardening Tool Steels
T74000-T75008	Cr-Steels Solid Welding Wire for Machinable Surfaces and Tool and Die Surfaces
T87510-T87520	Thermal Spray Wire
T90102-T91907	Cast Tool Steels