They All Look Like Copper. They Are Not.
RFQs for bushings, bearing sleeves, connector pins and contact parts come in with 'brass' written loosely — and the shop has to guess. Brass, bronze and copper are all copper alloys and all machinable, but they have opposite strengths. Spec the wrong one and you get a bushing that wears out in a month or a connector that loses its spring. Here is the practical breakdown from the shop floor.
Brass (C360): The Machinist's Friend
C360 free-cutting brass is the easiest metal to machine there is — excellent finish, tight tolerances, fast cycle times, low tool wear. It conducts electricity well and resists corrosion. That makes it the default for RF connector bodies, terminal pins, instrument parts and decorative hardware. The limits: brass is soft and not for heavy wear or high load. A brass bushing under constant load will wear faster than bronze.
Bronze (C932 / C954): Built to Slide
Bearing bronze (C932, SAE 660) has embedded lead and tin that make it self-lubricating — the classic material for bushings, wear plates and sliding components. Aluminum bronze (C954) is harder and stronger, used where high load and wear meet. Bronze costs more than brass and machines slower, but for a bushing that actually carries load, it is the difference between a part and a replacement part.
Pure Copper (C110): Conductivity First
Pure copper has the best electrical and thermal conductivity of the three, which is why it shows up in busbars, electrode components, heat sinks and high-current connectors. The trade-off: pure copper is gummy to machine — chips do not break cleanly, tolerances are harder to hold, and tool wear is higher. If the part only needs conductivity, copper is worth it. If it needs both conductivity and machinability, look at tellurium or leaded copper grades.
| Alloy | Best For | Machinability | Strength / Wear | Conductivity | Relative Cost |
|---|---|---|---|---|---|
| C360 brass | Connectors, fittings, terminals | Excellent | Low | Good | Low |
| C932 bearing bronze | Bushings, wear plates | Good | High | Moderate | Medium |
| C954 aluminum bronze | Heavy-load bearings | Fair | Very high | Moderate | High |
| C110 copper | Busbars, electrodes, contacts | Poor (gummy) | Low | Excellent | Medium |
Finishing and Plating
Copper alloys tarnish, so plating is common: nickel for wear and corrosion, silver or gold for connectors where contact resistance matters, tin for solderability. If the part is a contact or connector pin, the plating spec is as important as the base material — state it on the drawing. For bushings that run dry, some designs specify oil-impregnated sintered bronze instead of machined solid bronze; that is a different process, and the machined version is right when the geometry is precise.
If your drawing says 'brass' but the part carries load or conducts high current, we will flag it in the DFM review — and quote the right alloy the first time.
Tolerances in Copper Alloys: Soft Material, Sharp Numbers
Copper alloys expand roughly twice as much as steel per degree, and they are soft — both facts matter when tolerances are tight. A bushing with a 0.01 mm bore in bronze needs the measurement and the machining done at a consistent temperature, or the same part measures in and out of tolerance across the day. Soft materials also deflect under tool pressure, so fine bores and threads need sharp tooling and light finishing passes. None of this is a problem — it is routine — but it is why a tight-tolerance copper part costs more than an aluminum one. Hold your tightest features to the diameters that actually matter and the price stays sane.
Frequently Asked Questions
What is the difference between brass and bronze?
Brass is copper-zinc, easy to machine, good for connectors and fittings. Bronze is copper-tin, stronger and self-lubricating, built for bushings and wear parts.
Can brass be used for bushings?
For light duty, yes. Under continuous load or wear, use bearing bronze (C932) or aluminum bronze (C954) — they are built to slide.
Why is pure copper hard to machine?
It is soft and gummy — chips do not break, tolerances are harder to hold, and tools wear faster. Leaded or tellurium copper grades machine better.
Which copper alloy is best for RF connectors?
C360 brass is the standard — excellent machinability, good conductivity, and it plates well with nickel, silver or gold for contact performance.
Do copper alloy parts need plating?
Usually yes to prevent tarnishing — nickel for durability, silver or gold for low contact resistance on connectors, tin for solderability. State the plating spec on the drawing.