Unified numbering system

The unified numbering system (UNS) is an alloy designation system widely accepted in North America. It consists of a prefix letter and five digits designating a material composition. For example, a prefix of S indicates stainless steel alloys, C indicates copper, brass, or bronze alloys, T indicates tool steels, and so on. The first 3 digits often match older 3-digit numbering systems, while the last 2 digits indicate more modern variations. For example, Stainless Steel Type 310 in the original 3-digit system became S31000 in the UNS System. The more modern low-carbon variation, Type 310S, became S31008 in the UNS System. Often, the suffix digit is chosen to represent a material property specification. For example, "08" was assigned to UNS S31008 because the maximum allowed carbon content is 0.08%. The UNS is managed jointly by the ASTM International and SAE International. A UNS number alone does not constitute a full material specification because it establishes no requirements for material properties, heat treatment, form, or quality.

Some common materials and translations to other standards:

  • UNS K11547 is T2 tool steel
  • UNS S17400 is ASTM grade 630, Cr-Ni 17-4PH precipitation hardened stainless steel
  • UNS S30400 is SAE 304, Cr/Ni 18/10, Euronorm 1.4301 stainless steel
  • UNS S31600 is SAE 316
  • UNS S31603 is 316L, a low carbon version of 316. The digits "03" were assigned since the maximum allowed carbon content is 0.03%
  • UNS C90300 is CDA 903
UNS categories[1]
UNS series Metal type(s)
A00001 to A99999 Aluminum and aluminum alloys
C00001 to C99999 Copper and copper alloys (brasses and bronzes)
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
M1xxxx - Magnesium Alloys
N00001 to N99999 Nickel and nickel alloys
P00001 to P99999 Precious metals and alloys
R00001 to R99999 Reactive and refractory metals and alloys
R03xxx- Molybdenum Alloys
R04xxx- Niobium (Columbium) Alloys
R05xxx- Tantalum Alloys
R3xxxx- Cobalt Alloys
R5xxxx- Titanium Alloys
R6xxxx- Zirconium 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

See also


  1. Oberg, Erik; et al. (2004). Machinery's Handbook (27th ed.). Industrial Press Inc. p. 440. ISBN 0-8311-2700-7.
  2. Overview of the UNS system
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