Guides / Materials
C360 or C260: Why One Machines and the Other Does Not
September 21, 2026
Two yellow brasses, similar to look at, similar on a material list. One is the benchmark that every other metal’s machinability is measured against. The other is rated 30 on that same scale.
Understanding the difference stops a lot of expensive quotes.
The two alloys
| C360 free-cutting | C260 cartridge | |
|---|---|---|
| Copper | about 61.5 percent | about 70 percent |
| Zinc | about 35.5 percent | about 30 percent |
| Lead | 2.5 to 3.7 percent | trace |
| Machinability | 100 | 30 |
| Structure | alpha plus beta | single phase alpha |
| Made for | cutting | forming |
Published typical values for the alloy.
What the lead is actually doing
Lead does not dissolve into brass. It stays as tiny discrete soft particles distributed through the structure.
Those particles do two jobs at the cutting edge.
They act as crack initiators, so the chip breaks into short pieces instead of peeling off as a continuous ribbon.
They act as a lubricant, smearing across the tool face and reducing friction and built-up edge.
Take them away and you are cutting a ductile single phase alloy that wants to stretch rather than shear. That is C260.
What C260 is good at
It would be unfair to call C260 a bad alloy. It is an excellent alloy at a different job.
Single phase alpha brass is ductile and work hardens in a controlled way. It deep draws, spins, stamps and cold forms beautifully. The name comes from ammunition cases, which are drawn from flat blank to finished case in a series of operations that would tear most metals apart.
It also has better corrosion resistance than the higher zinc alpha-beta brasses in some environments, and it takes a good polish.
None of that helps a lathe.
What happens when you machine it anyway
Shops do machine C260. Here is what it costs.
Long chips. Continuous swarf wraps the tool and the part. On a bar-fed lathe running unattended this is not a nuisance, it is a crash risk, which means the machine needs watching and the economics change.
Poor finish. Ductile material smears rather than shearing cleanly, so the surface comes off with drag marks rather than a bright cut.
Burrs. Every exit edge, every cross hole. More hand work after the machine is done.
Shorter tool life and lower feasible feeds, so longer cycles.
Typical real world outcome: the same geometry costs somewhere between two and four times more in C260 than in C360, before any argument about bar price.
How to tell which one your drawing should carry
Ask one question: does anything happen to this part after machining that bends, draws, spins or crimps it?
No. The part is machined and then used. C360 is almost certainly right, and if the drawing says C260 it is worth asking why.
Yes. The formability is real and C260 may be correct. Accept the machining cost, or discuss splitting the process differently with the shop.
The most common case we see is the first one wearing the second one’s clothes. A part that was originally stamped gets redesigned as a machined component, the material field on the drawing is copied across unchanged, and nobody notices that the reason for the material left with the old process.
The drinking water trap
C260 carries only trace lead, so it comfortably clears the 0.25 percent weighted average limit in NSF/ANSI 372.
That does not make it a good potable water alloy.
At 30 percent zinc it has poor dezincification resistance, and dezincification is the dominant failure mode in water systems. A fitting that passes the lead rule and then loses its zinc in three years has not solved the problem. See dezincification resistant brass and NSF/ANSI 61 and 372.
For drinking water, C69300 silicon brass answers both questions at once: under 0.09 percent lead, highly dezincification resistant, machinability 80.
The stress corrosion note
C260 is frequently cold formed, and cold forming leaves residual tensile stress. Residual stress plus ammonia equals stress corrosion cracking in brass.
If your part is drawn or formed and then lives anywhere near ammonia, amines or cleaning chemicals, a stress relief anneal belongs on the drawing. See season cracking in brass parts.
The summary
C360 is for cutting. C260 is for forming. They are not grades of the same thing, they are different tools.
If your machined part carries C260 and nothing is formed after machining, changing to C360 is usually the single cheapest improvement available to that drawing.
For the wider picture across the brass family, see which brass alloy to specify.
Not sure which your part should be? Send the drawing, say what happens to the part after machining, and leave the grade as Not sure.
Frequently asked questions
Can a shop machine C260 if I insist?
Yes, and it will cost several times more and the surface finish will be worse. C260 is ductile and does not break its chip, so it produces long stringy swarf that wraps the tool and scores the part. If the drawing does not need the formability, changing to C360 usually lowers the price without changing anything that matters.
Why would anyone specify C260 for a machined part?
Usually because the design started as a stamped or deep drawn part and later moved to machining without anyone revisiting the material. Occasionally because the part is machined and then formed, in which case the formability is genuinely needed. It is always worth asking which of the two it is.
Is C260 lead-free?
It carries only trace lead, so it is well under the 0.25 percent weighted average limit in NSF/ANSI 372. That does not make it a good potable water alloy, because it has poor dezincification resistance. For drinking water use C69300 silicon brass, which is both lead-free and dezincification resistant.
What is the nearest machinable equivalent to C260?
There is no direct equivalent, because the properties trade against each other. If you need deep drawing, C260 is right and machining will be expensive. If you need machining and only moderate ductility, C360 is right. If you need both formability and better machining than C260, talk to the shop about C272 or a controlled temper, and expect a compromise.
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