Copper or Brass for a Contact, Terminal or Connector Body
September 26, 2026
Copper and brass both show up in connectors, terminals and contacts, and the choice is often made by habit or by what the last part was. The tradeoff is simple and it is worth making deliberately.
The numbers
| C11000 copper | C14500 free-machining copper | C36000 free-cutting brass | |
|---|---|---|---|
| Conductivity | About 100 percent IACS | About 93 percent IACS | About 26 percent IACS |
| Machinability | 20 | 85 | 100 |
| Threads and fine features | Difficult | Good | Excellent |
| Strength | Low | Low | Moderate |
| Plating | Good, after cleaning | Good | Excellent |
| Lead content | None | None | Yes, check RoHS |
| Relative material cost | Higher | Higher | Lower |
Published typical values for the alloys, not a promise from any shop.
Where brass belongs
Brass conducts about a quarter as well as copper. That sounds disqualifying and often is not.
A connector body 20 millimetres long carries current over a short path with a large cross section. Its contribution to circuit resistance is tiny in either material. Meanwhile it has threads, a knurl, a cross hole and a plated face, and every one of those is far cheaper in brass. This is why so much connector hardware is brass and why that is a sound decision rather than a compromise.
Brass belongs where the part is small, the current path is short, the current is modest and the geometry is feature heavy.
Where copper belongs
Copper belongs where the part is actually part of the conductor rather than just holding one.
Busbars, lugs carrying full circuit current, high current terminals, contacts that run warm, anything with a specified contact resistance, and anything where a temperature rise is calculated on the assumption of copper. On those parts brass raises resistance, raises temperature and can fail a rating that copper would pass.
Copper also belongs everywhere brass is excluded by the lead content: potable water, some medical and food contact applications and any market with strict RoHS exposure. See C36000 for the lead question.
The middle option most people miss
Free-machining copper exists precisely for this decision. C14500 tellurium copper machines nearly as well as brass and conducts above 90 percent IACS. It gives you threads that come out clean and cross holes that do not need an hour of deburring, on a part that is still a real conductor.
If your part has features and carries current, this is usually the answer, and it is usually not the one on the drawing. Reference page: C14500.
Deciding in one pass
- Is the part a significant share of the circuit resistance, or does it have a contact resistance or temperature specification? Copper, and probably C11000.
- Does it carry real current and have threads, cross holes or fine features? Free-machining copper, C14500.
- Is it small, short, modest current and feature heavy, with no lead restriction? Brass, C36000.
- Is lead excluded? Not brass. C14500 or C11000 depending on the geometry.
Plating changes nothing about the base
Both materials are plated for contact surfaces. Plating does not fix the conductivity of the base metal, it only fixes the surface. A brass terminal with silver plating still has brass resistance through its body. See tin, nickel and silver plating.
What to write on the drawing
State the property, not the habit. “Minimum 90 percent IACS” lets a shop offer C14500. “Copper or brass, RoHS compliant” tells it brass is out. “C36000” tells it nothing about why, and you will get C36000 whether or not it was right.
How to specify copper on a drawing covers the callout. The RFQ builder writes it.
Frequently asked questions
Is brass good enough for electrical contacts?
For many connector bodies and low current terminals, yes. Brass at about 26 percent IACS is fine where the part is short and the current is modest. It is the wrong choice where the part carries significant current, runs warm or where contact resistance is specified.
Why do connector manufacturers use brass so much?
Because it machines quickly, holds threads and fine features well, and takes plating cleanly. On a small part the conductivity penalty is a fraction of a milliohm and the machining saving is large.
What is the middle option?
Free-machining copper, C14500 or C14700. Roughly brass machinability with above 90 percent IACS. It is the answer for a part that needs real conductivity and has threads or cross holes.
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