The Structure of UNS C-Series Numbers
Every wrought or cast copper alloy registered in the Unified Numbering System is identified by the letter C followed by a five-digit number running from C00001 to C99999. The first digit identifies the alloy family. The remaining digits separate individual compositions within that family and, in the copper system, also carry the wrought versus cast distinction. Learning to read the string left to right turns a five-digit code into a short material specification.
What the First Digit Means
| Range | Family | Representative grade |
|---|---|---|
| C1xxxx | High-copper alloys, 99.3% Cu and above | C11000 electrolytic tough pitch copper |
| C2xxxx | Copper-zinc alloys, the brasses | C26000 cartridge brass, 70/30 |
| C3xxxx | Copper-zinc-lead alloys, free-machining brasses | C36000 free-cutting brass |
| C4xxxx | Copper-zinc-tin alloys, the tin brasses | C46400 naval brass |
| C5xxxx | Copper-tin alloys, phosphor and tin bronzes | C51000 phosphor bronze, 5% tin |
| C6xxxx | Copper-aluminium, copper-silicon and copper-nickel alloys | C70600 copper-nickel 90/10 |
| C7xxxx | Other alloys, including the nickel silvers | C75200 nickel silver 65/18 |
| C8xxxx and C9xxxx | Cast alloys and ingots | C93200 SAE 660 bearing bronze, cast |
The family digit is the fastest screening tool available. Two enquiries that quote C26000 and C51000 are asking for very different metals: a ductile, deep-drawing brass and a spring-tempered phosphor bronze. Reading the first digit avoids that confusion before a quotation is prepared.
Wrought versus Cast: Reading the Last Digits
In the copper system, wrought alloys, that is those rolled, drawn or extruded, carry numbers ending in 01 through 99 within the C1xxxx to C7xxxx blocks. Cast alloys are designated in the C8xxxx and C9xxxx ranges, with cast copper and ingot series ending in 00 or using suffixes in the 90 to 99 band. C11000 is therefore wrought electrolytic tough pitch copper, while C93200 is a cast bearing bronze. The same nominal family can appear twice, because a wrought brass and its cast counterpart carry different five-digit codes and different mechanical properties.
Decoding Common Grades
C11000 electrolytic tough pitch copper, the electrical conductor and tubing workhorse.
C12200 deoxidized high-phosphorus copper, the standard grade for copper water tube.
C26000 cartridge brass, 70% copper and 30% zinc, deep-drawing quality.
C36000 free-cutting brass, the benchmark for machined fittings and hardware.
C51000 phosphor bronze with 5% tin, used for springs and corrosion service.
C70600 copper-nickel 90/10, used for seawater piping and condenser service.
C93200 leaded tin bronze, a general-purpose cast bearing alloy.
Note the pairing rule in practice: a designer who needs a wrought tube and a cast fitting for the same assembly will specify two different C-numbers even though both are, for example, brasses. Substituting one for the other changes strength, machinability and corrosion behaviour.
How This Differs from Chinese GB Designations
Chinese national standards use an entirely separate naming logic. Pure copper grades are written T1, T2 and T3 by residual oxygen and purity. Brasses are named by nominal zinc content, as in H65, H62 and H59. Bronzes are named by the main alloying element with a composition figure, as in QSn6.5-0.1 and QAl10-3-1.5. White copper follows the same idea, as in BFe10-1-1. The two systems are not interchangeable, and a grade name alone is never enough to place an order.
The practical rule is to quote the specification standard rather than the grade, for example ASTM B280 for air-conditioning and refrigeration tube, ASTM B16 for free-cutting brass rod, ASTM B124 for copper alloy forging stock, or the corresponding GB/T standard. The standard fixes the chemistry limits, temper, tolerances and test methods, while the grade name only points at an intended family. When the two conflict, the standard governs.
Frequently Asked Questions
Q: What does the letter C mean in a copper alloy designation?
It marks the alloy as a copper-base material registered in the Unified Numbering System; the following five digits identify the family and the individual composition.
Q: How can wrought and cast copper alloys be told apart by number?
Wrought alloys sit in the C1xxxx to C7xxxx blocks, while cast alloys are placed in the C8xxxx and C9xxxx ranges.
Q: Is C11000 the same as C12200?
No. C11000 is electrolytic tough pitch copper, while C12200 is deoxidized high-phosphorus copper used where hydrogen embrittlement in brazing or welding must be avoided.
Q: Are UNS C-numbers and Chinese GB grades interchangeable?
No. They are separate systems; T2, H62 or QSn6.5-0.1 cannot be substituted for a C-number without checking the controlling standard for chemistry and properties.
Q: Does the last two digits always indicate cast versus wrought?
Only in combination with the family digit: a trailing 00 or a 90 to 99 suffix in the cast blocks signals cast or ingot material, while 01 to 99 within the earlier blocks indicates wrought product.
Q: Why quote the standard instead of just the grade?
Because the standard controls chemistry limits, temper, tolerances and testing, and it removes ambiguity when the same common name is used differently in different markets.
