Unified Numbering System (UNS)

The Unified Numbering System (UNS) is an alloy designation system widely accepted in American markets. It consists of a prefix letter and five numbers designating a material composition. A prefix S stands for stainless steel alloys, C for copper, brass or bronze alloys, T for tool steels, etc.

The first three digits often correspond to older three-digit numbering systems, while the last two digits indicate more modern variants. For example, copper alloy No. 377 (wrought brass) in the original three-digit system became C37700 in the UNS system.

UNS series	Metal type(s)
A00001 to A99999	Aluminum and aluminum alloys
C00001 to C99999	Copper and copper alloys
D00001 to D99999	Specified mechanical property steels
E00001 to E99999	Rare earth and rare earthlike metals and alloys
F00001 to F99999	Cast irons
G00001 to G99999	AISI and SAE carbon and alloy steels (except tool steels)
H00001 to H99999	AISI and SAE H-steels
J00001 to J99999	Cast steels (except tool steels)
K00001 to K99999	Miscellaneous steels and ferrous alloys
L00001 to L99999	Low-melting metals and alloys
M00001 to M99999	Miscellaneous nonferrous metals and alloys
N00001 to N99999	Nickel and nickel alloys
P00001 to P99999	Precious metals and alloys
R00001 to R99999	Reactive and refractory metals and alloys
S00001 to S99999	Heat and corrosion resistant (stainless) steels
T00001 to T99999	Tool steels, wrought and cast
W00001 to W99999	Welding filler metals
Z00001 to Z99999	Zinc and zinc alloys

The UNS is jointly administered by ASTM International and SAE International. A UNS number alone does not constitute a complete material specification because it does not specify requirements for material properties, heat treatment, shape or quality.

Some examples of commonly used materials..

UNS S31603 - Type 316/316L is a molybdenum-containing austenitic stainless steel intended to provide improved corrosion resistance relative to Type 304/304L in moderately corrosive process environments, particularly those containing chlorides or other halides.

UNS S17400 - Alloy 17-4PH Type 630, is a chromium-nickel-copper precipitation-hardening martensitic stainless steel with an addition of niobium. 17-4PH combines high strength and hardness with good corrosion resistance.

UNS A91100 - Is an aluminium-based alloy in the commercially pure wrought family. With a minimum of 99.0% aluminium, it is the most heavily alloyed of the 1000 series. It is also the mechanically strongest alloy in the series, and is the only 1000-series alloy commonly used in rivets.

UNS M11311 - Magnesium AZ31B alloy is available in different forms such as plate, sheet, and bar. It is an alternative to aluminum alloys as it has high strength to weight ratio. It is widely available when compared to other magnesium grades.