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Copper Grade Reference for Machining

Fourteen grades, what each one is for, and the exact specification line to put on a drawing. Written for the person who has to decide before the RFQ goes out.

"Copper" is not a specification

Across this table, conductivity runs from 22 to 101 percent IACS and machinability runs from 20 to 85. Those are different materials doing different jobs. A drawing that says copper hands the choice to whoever is buying the bar that week.

The UNS number removes the ambiguity in five characters. Copper alloys sit in the C1xxxx to C7xxxx range, and machined work lives almost entirely in two of those blocks:

C1xxxx coppers, at least 99.3 percent copper, including the free-machining and age hardening grades
C3xxxx leaded brasses, which is where the machinability reference point sits

Everything below is one of those two, plus the small number of high strength coppers that get machined regularly.

The full table

Conductivity is percent IACS. Machinability is rated against free-cutting brass C36000 at 100. Published typical values for the alloy, not a promise from any shop.

UNS	Name	%IACS	Mach.	Usual temper	What it is for
C10100	Oxygen free electronic copper OFE, OFHC, C101	101	20	O61 annealed, or H02 half hard	Ultra high vacuum parts, hydrogen brazed assemblies, sinker EDM electrodes, RF and cryogenic components.
C10200	Oxygen free copper OF, C102	101	20	O61 annealed, or H02 half hard	Oxygen free work that does not need the tighter purity control of C10100.
C11000	Electrolytic tough pitch copper ETP, C110	100	20	H02 half hard for busbar, O61 annealed where it gets bent	The default electrical copper. Busbars, terminals, lugs, contact blocks, cold plates, heat sinks.
C12200	Phosphorus deoxidized copper, high residual DHP, C122	85	20	O60 annealed, or H55 light drawn for tube	Tube, pipe and fabricated parts that get brazed or welded. Standard plumbing and refrigeration copper.
C14500	Tellurium copper TeCu, C145	93	85	H04 hard drawn for turned parts	Turned parts, threaded components, connector bodies, terminals, fittings. Anything feature heavy.
C14700	Sulphur copper SCu, C147	95	85	H04 hard drawn	The same job as C14500 where a little more conductivity is wanted.
C18700	Leaded copper C187	96	85	H04 hard drawn	High volume screw machine work where free-machining behaviour and conductivity are both needed.
C15000	Zirconium copper CuZr, C150	93	20	TH04 precipitation hardened and cold worked	Resistance welding electrodes for aluminum and coated steel, and parts that must stay conductive while hot.
C18150	Chromium zirconium copper CuCrZr, C18150	80	20	TH04 precipitation hardened and cold worked	Welding electrodes and holders, high duty contacts, parts that see heat and load together.
C18200	Chromium copper CuCr, C182	80	20	TH04 precipitation hardened and cold worked	The general purpose resistance welding electrode material. Also mould inserts and hot stiff parts.
C17510	Nickel beryllium copper CuNiBe, C17510	45 to 60	20	TF00 precipitation hardened	Welding electrode holders, high conductivity springs, parts needing strength with moderate conductivity.
C17200	Beryllium copper CuBe, BeCu, C172	22	20	TB00 solution treated for machining, TF00 or TH04 on the finished part	Spring contacts, connectors, non-sparking tools, mould inserts, high fatigue components.
C26000	Cartridge brass 70/30 brass, C260	28	30	H02 half hard	Formed and drawn parts. Listed here because it is often confused with a machining brass.
C36000	Free-cutting brass C360, 360 brass	26	100	H02 half hard	The reference point for the machinability scale, and the default when conductivity does not matter.

Pure coppers

Above 99.9 percent copper. You specify these when a conductivity, thermal or vacuum number is on the print, and you pay for them in machining time.

C10100 Oxygen free electronic copper

Conductivity: 101 percent IACS
Machinability: 20
Specification: ASTM B152 (sheet, strip, plate, rolled bar), ASTM B187 (bus bar, rod, bar, shapes)
Usual temper: O61 annealed, or H02 half hard

Use it for. Ultra high vacuum parts, hydrogen brazed assemblies, sinker EDM electrodes, RF and cryogenic components.

Watch out. Costs more than C110 and buys about one point of conductivity. Specify it for the oxygen content, not for the conductivity.

Drawing callout

Oxygen free electronic copper, UNS C10100, [ASTM spec for your product form], temper O61 annealed

C10200 Oxygen free copper

Conductivity: 101 percent IACS
Machinability: 20
Specification: ASTM B152 (sheet, strip, plate, rolled bar), ASTM B187 (bus bar, rod, bar, shapes)
Usual temper: O61 annealed, or H02 half hard

Use it for. Oxygen free work that does not need the tighter purity control of C10100.

Watch out. Often quoted interchangeably with C10100 by stockists. If the purity level matters to your application, say which one on the drawing.

Drawing callout

Oxygen free copper, UNS C10200, [ASTM spec for your product form], temper O61 annealed

C11000 Electrolytic tough pitch copper

Conductivity: 100 percent IACS
Machinability: 20
Specification: ASTM B152 (sheet, strip, plate, rolled bar), ASTM B187 (bus bar, rod, bar, shapes)
Usual temper: H02 half hard for busbar, O61 annealed where it gets bent

Use it for. The default electrical copper. Busbars, terminals, lugs, contact blocks, cold plates, heat sinks.

Watch out. Contains a small amount of oxygen as copper oxide. Heat it in hydrogen and it embrittles, so it is the wrong grade for hydrogen furnace brazing and for ultra high vacuum.

Drawing callout

Electrolytic tough pitch copper, UNS C11000, [ASTM spec for your product form], temper H02 half hard for busbar

C12200 Phosphorus deoxidized copper, high residual

Conductivity: 85 percent IACS
Machinability: 20
Specification: ASTM B152 (sheet, strip, plate), ASTM B75 (tube), ASTM B42 (pipe)
Usual temper: O60 annealed, or H55 light drawn for tube

Use it for. Tube, pipe and fabricated parts that get brazed or welded. Standard plumbing and refrigeration copper.

Watch out. The phosphorus that makes it weldable costs you about 15 points of conductivity. Do not use it where the electrical number matters.

Drawing callout

Phosphorus deoxidized copper, high residual, UNS C12200, [ASTM spec for your product form], temper O60 annealed

Free-machining coppers

A small addition breaks the chip. Around four times the machinability of pure copper for a few points of conductivity, which is the best trade available in this material family.

C14500 Tellurium copper

Conductivity: 93 percent IACS
Machinability: 85
Specification: ASTM B301 (free-cutting copper rod, bar, wire and shapes)
Usual temper: H04 hard drawn for turned parts

Use it for. Turned parts, threaded components, connector bodies, terminals, fittings. Anything feature heavy.

Watch out. The single largest cost lever in copper machining. Roughly four times the machinability of pure copper for about seven points of conductivity. Not for ultra high vacuum.

Drawing callout

Tellurium copper, UNS C14500, [ASTM spec for your product form], temper H04 hard drawn for turned parts

C14700 Sulphur copper

Conductivity: 95 percent IACS
Machinability: 85
Specification: ASTM B301 (free-cutting copper rod, bar, wire and shapes)
Usual temper: H04 hard drawn

Use it for. The same job as C14500 where a little more conductivity is wanted.

Watch out. Thinner on the ground than C14500. Check stock and lead time before you specify it.

Drawing callout

Sulphur copper, UNS C14700, [ASTM spec for your product form], temper H04 hard drawn

C18700 Leaded copper

Conductivity: 96 percent IACS
Machinability: 85
Specification: ASTM B301 (free-cutting copper rod, bar, wire and shapes)
Usual temper: H04 hard drawn

Use it for. High volume screw machine work where free-machining behaviour and conductivity are both needed.

Watch out. Contains around 1 percent lead. Check RoHS and REACH exposure for your market before specifying it, and expect some buyers to reject it on that basis alone.

Drawing callout

Leaded copper, UNS C18700, [ASTM spec for your product form], temper H04 hard drawn

High strength and heat resistant coppers

Age hardened alloys chosen for strength, hardness or hot performance. Conductivity drops, sometimes a long way, and none of them machine quickly.

C15000 Zirconium copper

Conductivity: 93 percent IACS
Machinability: 20
Specification: Specification depends on product form, confirm with the supplier. RWMA Class 1.
Usual temper: TH04 precipitation hardened and cold worked

Use it for. Resistance welding electrodes for aluminum and coated steel, and parts that must stay conductive while hot.

Watch out. Keeps most of copper’s conductivity and gains real high temperature strength. Softens if it is overheated in service or in machining.

Drawing callout

Zirconium copper, UNS C15000, [ASTM spec for your product form], temper TH04 precipitation hardened and cold worked

C18150 Chromium zirconium copper

Conductivity: 80 percent IACS
Machinability: 20
Specification: Specification depends on product form, confirm with the supplier. RWMA Class 2.
Usual temper: TH04 precipitation hardened and cold worked

Use it for. Welding electrodes and holders, high duty contacts, parts that see heat and load together.

Watch out. Holds strength at higher temperature than C18200. Both are Class 2 and are frequently substituted for one another, so say which one you need.

Drawing callout

Chromium zirconium copper, UNS C18150, [ASTM spec for your product form], temper TH04 precipitation hardened and cold worked

C18200 Chromium copper

Conductivity: 80 percent IACS
Machinability: 20
Specification: Specification depends on product form, confirm with the supplier. RWMA Class 2.
Usual temper: TH04 precipitation hardened and cold worked

Use it for. The general purpose resistance welding electrode material. Also mould inserts and hot stiff parts.

Watch out. Age hardened, so machining before or after heat treatment changes both the cycle time and the final dimensions. Say which dimensions are critical.

Drawing callout

Chromium copper, UNS C18200, [ASTM spec for your product form], temper TH04 precipitation hardened and cold worked

C17510 Nickel beryllium copper

Conductivity: 45 to 60 percent IACS
Machinability: 20
Specification: ASTM B441 (rod and bar). RWMA Class 3.
Usual temper: TF00 precipitation hardened

Use it for. Welding electrode holders, high conductivity springs, parts needing strength with moderate conductivity.

Watch out. Conductivity varies widely with temper, so quote the temper alongside the grade or you are not specifying anything.

Drawing callout

Nickel beryllium copper, UNS C17510, [ASTM spec for your product form], temper TF00 precipitation hardened

C17200 Beryllium copper

Conductivity: 22 percent IACS
Machinability: 20
Specification: ASTM B194 (plate, sheet, strip, rolled bar), ASTM B196 (rod and bar)
Usual temper: TB00 solution treated for machining, TF00 or TH04 on the finished part

Use it for. Spring contacts, connectors, non-sparking tools, mould inserts, high fatigue components.

Watch out. A structural alloy that happens to conduct, not a conductor. Machining generates particulate that requires shop controls, so say it is beryllium copper in the RFQ.

Drawing callout

Beryllium copper, UNS C17200, [ASTM spec for your product form], temper TB00 solution treated for machining

Brasses, for reference

Not copper, listed so the machinability scale has a fixed point and so the two most commonly confused brasses are not specified by accident.

C26000 Cartridge brass

Conductivity: 28 percent IACS
Machinability: 30
Specification: ASTM B19 (strip), ASTM B36 (sheet, strip, plate, bar)
Usual temper: H02 half hard

Use it for. Formed and drawn parts. Listed here because it is often confused with a machining brass.

Watch out. It is a forming brass, not a free-machining one. Its machinability rating is 30, nowhere near C36000.

Drawing callout

Cartridge brass, UNS C26000, [ASTM spec for your product form], temper H02 half hard

C36000 Free-cutting brass

Conductivity: 26 percent IACS
Machinability: 100
Specification: ASTM B16 (rod, bar and shapes for screw machines)
Usual temper: H02 half hard

Use it for. The reference point for the machinability scale, and the default when conductivity does not matter.

Watch out. Leaded. Check RoHS exposure. It conducts about a quarter as well as copper, so it is not a substitute for a conductor.

Drawing callout

Free-cutting brass, UNS C36000, [ASTM spec for your product form], temper H02 half hard

Temper codes you will actually use

Temper designations follow ASTM B601. A grade without a temper is an incomplete specification on anything that gets bent, and on every age hardening alloy.

Code	Name	What it means for your part
O60	Soft anneal	Fully annealed. Bends easily, machines gummily, marks easily in the vise.
O61	Annealed	The usual annealed condition for rod, bar and plate.
H01	Quarter hard	Light cold work. A compromise where the part is both bent and machined.
H02	Half hard	The default for busbar and machined plate. Stiffer, cuts a little better, needs a larger bend radius.
H04	Hard	Standard for drawn free-machining rod. Best surface finish, worst formability.
TB00	Solution heat treated	Age hardenable alloys in the soft condition. Machine now, harden later, accept a small dimensional change.
TD04	Solution treated and cold worked, hard	Strength before ageing.
TF00	Precipitation hardened	Fully aged. Final properties, slower to cut, dimensions hold.
TH04	Cold worked and precipitation hardened	The usual delivery condition for welding electrode alloys.

Pick a grade from the requirement

Work down this list and stop at the first line that describes your part. It resolves most copper specifications in one pass.

Ultra high vacuum, or brazed in hydrogenC10100. No substitution. Free-machining grades are contaminants in this context.
A conductivity or thermal number on the printC11000. Specify C10100 only if you can name the oxygen related reason.
Feature heavy, threads or cross holes, conductivity has headroomC14500, or C14700 for a little more conductivity. This is the cheapest copper part you can design.
Resistance welding electrode, aluminum or coated steelC15000, RWMA Class 1.
Resistance welding electrode, general purposeC18200 or C18150, RWMA Class 2. Say which.
Strength, fatigue life or springiness firstC17200. Declare it as beryllium copper in the RFQ so unequipped shops decline early.
Brazed or welded tube and fabricationC12200. Accept the conductivity loss, it is the price of weldability.
Conductivity genuinely does not matterC36000 brass, and check RoHS exposure on the lead.

Still unsure? Write the requirement on the drawing and leave the grade open. A shop can then offer the cheapest alloy that meets it, which is usually a better outcome than guessing.

How to write the callout

Four elements, in this order. Anything missing is a decision you have handed to a stranger.

Electrolytic tough pitch copper,
UNS C11000,
ASTM B187 (bus bar, rod, bar and shapes),
temper H02

Material name so a human reading it knows what it is
UNS number so there is no ambiguity
ASTM specification for your product form. Bar, rod, sheet and tube are different standards for the same alloy
Temper per ASTM B601

Add "no substitution" when a substitution would break the part, or the requirement in plain numbers when you are open to one.

Questions about grades

Something missing from this reference? Email and we will add it. Terms are defined in the glossary.

Is it enough to write "copper" on a drawing?

No. Copper covers alloys whose conductivity runs from 22 to 101 percent IACS and whose machinability runs from 20 to 85. A shop asked for "copper" will quote whatever it can buy, and you may receive a part that performs nothing like the one you designed. Write the UNS number.

What is the difference between C101 and C110?

C10100 is oxygen free and C11000 contains a small amount of oxygen as copper oxide. In conductivity the gap is about one point, which almost never changes a design. The real difference is that C11000 embrittles when heated in hydrogen and is unsuitable for ultra high vacuum, so those two applications force C10100.

Which copper grade machines fastest?

The free-machining coppers, C14500 tellurium and C14700 sulphur, at a machinability rating near 85 against pure copper at 20. They hold above 90 percent IACS, which is why they are the first thing to consider when a copper part is feature heavy.

Do I need to specify a temper as well as a grade?

Yes on anything that gets bent, and on any age hardening alloy. Temper changes strength, bend radius, machining behaviour and, on the beryllium and chromium coppers, conductivity. A grade without a temper is an incomplete specification.

Can a shop substitute an equivalent grade?

Only if you let it. If you are open to a substitution, write the requirement next to the grade, for example minimum 90 percent IACS. A shop can then offer a cheaper alloy that still meets it. If substitution would break the part, say no substitution on the drawing.

Where do these numbers come from?

Published alloy data, principally the Copper Development Association, plus ASTM specifications for product form and temper and RWMA classes for welding electrode materials. They are typical values for the alloy and not a commitment from any shop. Our sourcing rules are on the editorial standards page.

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