C110 vs C145: Which Copper Should Your Part Be
September 26, 2026
Most copper parts that are not vacuum or welding electrodes end up as one of two grades. This is the comparison that decides which, and it is shorter than people expect because the two alloys differ on almost exactly one axis.
The numbers
| C11000 ETP | C14500 tellurium | |
|---|---|---|
| Conductivity | About 100 percent IACS | About 93 percent IACS |
| Machinability | 20 | 85 |
| Chip | Long, continuous, gummy | Short, breaks cleanly |
| Burrs | Heavy, hand work | Light |
| Threads and cross holes | Difficult, risk at tapping | Clean |
| Usual temper | H02 half hard | H04 hard drawn |
| Specification | ASTM B187 bar, B152 plate | ASTM B301 |
| Stock | Everywhere | Thinner, check lead time |
| Vacuum service | Not for UHV either | No, tellurium is a contaminant |
Published typical values for the alloys, not a promise from any shop.
What C145 buys you
About four times the machinability rating, for the price of about seven points of conductivity.
In practice that means turned parts that come off the machine with clean threads and clean holes, far less hand deburring, and cycle times that can drop by half or more on feature heavy work. It is the single largest cost lever in copper machining and it costs nothing to design in. The mechanism is covered in how copper behaves in milling, turning, drilling and tapping.
What C110 keeps
The last seven points of conductivity, wide stock availability, and the fact that most electrical standards and most buyer habits already assume it.
It also keeps the machining problems. Burrs on every edge, chips that wrap, tapping as the operation where parts get scrapped.
Decide by the part, not the material
A turned connector body with threads and cross holes. C145. This is what free-machining copper was made for. Staying on C110 here is paying for cycle time and deburring that buy you nothing.
A busbar. C110. The part is mostly metal and a little machining. The free-machining benefit is small and the conductivity loss is a real cost on every amp for the life of the assembly. See the busbar design guide.
A heat sink. C110. Thermal conductivity is the whole point of the part. Do not give any of it away.
A terminal or lug with a few holes. Usually C145 if the electrical requirement has headroom. Write the requirement and let the shop choose.
Anything with a certified conductivity requirement, or in vacuum. C110 or C101. C145 is not an option.
The drawing line that ends the argument
If you are unsure, do not pick. Write the property:
Copper, minimum 90 percent IACS.
C11000 preferred, C14500 accepted.A shop reading that can quote both and tell you the difference. A shop reading “C110” will quote C110 and you will never learn what the part could have cost. How to specify copper on a drawing covers the full callout.
Two mistakes to avoid
Specifying C145 for vacuum or brazed parts. Tellurium is a contaminant in those contexts. The grade decision there is made by physics, not by cost.
Assuming C145 is always in stock. It is not, and the bar can take longer than the machining. See copper lead times.
Both grades have their own reference page: C11000 and C14500. The three way comparison including C101 is in C101 vs C110 vs tellurium copper.
Frequently asked questions
How much cheaper is a C145 part than the same part in C110?
It depends on how much of the price is machining. On a feature heavy turned part the machining line can fall by half or more. On a plain busbar, where the price is mostly metal, the saving is small and the conductivity loss is not worth it.
Is C145 conductive enough for a busbar?
At about 93 percent IACS it usually is, electrically. But a busbar is mostly metal with little machining, so the free-machining benefit is small there and most busbar is C110 by convention and by the standards it is built to.
Can I let the shop choose between them?
Yes, and it is the best option when you are unsure. Write the requirement as minimum 90 percent IACS and mark substitution as accepted. A shop can then quote C145 honestly.
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