Brass vs Bronze vs Copper: Picking a Copper Alloy

One base metal, three jobs

Copper is the starting point for all three materials, and the differences between them are differences of alloying.

Copper on its own is soft, highly conductive and highly ductile. It is difficult to machine well and expensive, and it is chosen for exactly one dominant property: it carries current and moves heat better than any of the alternatives at a reasonable cost.

Brass is copper with zinc added, usually between about 30% and 40%. Zinc is cheap, and adding it raises strength, improves machinability dramatically, and produces the familiar yellow-gold colour. Brass is the workhorse of the copper family and the material behind most turned fittings, valves and fasteners.

Bronze is copper with tin added, and often with other elements such as aluminium, phosphorus or lead depending on the family. Bronze is stronger than brass, more corrosion resistant, and it has one property that neither of the others shares: it works as a bearing surface against steel.

	Copper	Brass	Bronze
Alloying	None (base metal)	Zinc	Tin, plus other elements
Common grades	C110 (ETP), C101 (OFE)	C360 free-cutting, C260 cartridge	Bearing bronze, aluminium bronze
Colour	Reddish	Yellow-gold	Red-brown to brownish
Machinability	Poor — gummy, smears	Excellent — C360 is the 100% reference	Moderate
Electrical conductivity	~100% IACS	~28% IACS	Low
Thermal conductivity	Highest	Lower	Lower
Strength	Low	Moderate	Higher
Bearing behaviour	Not a bearing material	Not a bearing material	Excellent against steel
Seawater	Good	Vulnerable to dezincification	Very good
Contains lead	No	C360 does; C260 does not	Some families do
Relative material cost	Highest	Lowest	Middle

Why the alloying element decides everything

Zinc and tin do completely different things to copper, and the differences explain almost every practical question about these three materials.

Zinc is cheap, it forms a solid solution with copper that is easy to cast and machine, and it raises strength moderately. It also makes the alloy dramatically easier to cut — free-cutting brass is the easiest metal on the shop floor to machine — and it lowers the melting point, which makes brass the natural choice for cast and hot-worked parts.

Tin is expensive and it does something zinc cannot: it produces an alloy that behaves well when sliding against steel. The tin and lead in a bearing bronze create a structure that will run against a steel shaft, bedding in slightly and holding a film of lubricant, without galling or picking material off the shaft. No amount of brass or copper does that.

So the three materials map onto three requirements:

• Carry current or move heat — copper
• Be machined accurately and cheaply — brass
• Run as a bearing, or survive seawater — bronze

Where a part has more than one of those requirements, the design usually changes rather than the alloy. A conductive bushing becomes a copper insert in a bronze body, or a bronze bushing with a copper conductor beside it.

Machinability: brass is the yardstick

Machinability ratings for metals are quoted relative to free-cutting brass, which is set at 100%. That tells you how far ahead of everything else brass sits.

C360 free-cutting brass cuts at very high spindle speeds with short, broken chips. It holds fine detail, threads cleanly with minimal burr, and produces a good surface straight off the tool. On a high-volume turned part there is nothing faster, and the cycle time reflects it.

C260 cartridge brass is the other common grade and behaves very differently despite being in the same family. It is not a free-cutting grade — it is chosen for ductility and cold formability, and parts made from it are usually formed rather than machined. Where a brass part is deep drawn, stamped or cold headed, C260 is the candidate, not C360.

Bronze machines less freely than free-cutting brass. The bearing bronzes are formulated for their sliding behaviour, not their cutting behaviour, and the tool load is higher and the finish more difficult to control. The cycle time on a bronze bushing reflects that.

Copper is the difficult one. It is soft and ductile, so it smears and burrs rather than shearing cleanly, it drags on the tool, and it builds up on the cutting edge. Threading and fine details need careful planning, and the contact faces have to be kept clean. The extra care shows in the unit cost, which is the reason copper is reserved for parts where conductivity is the actual requirement — see brass and copper machined parts for how the grades we run behave on the floor.

The lead question

Free-cutting brass C360 contains lead, typically around 2.5–3.5%, and the lead is not an impurity — it is the mechanism. Dispersed as fine particles through the alloy, it acts as an internal lubricant and chip breaker at the cutting edge, and it is what earns C360 its 100% machinability rating.

That also means C360 is affected by lead restrictions. Where RoHS or a similar specification applies, the lead content puts the grade in scope, exactly as it does for leaded steel — the same problem, the same question, in a different alloy system. We covered the steel version in the 12L14 vs 1215 comparison, and the logic repeats here:

• C360 contains lead and does not satisfy a lead restriction.
• C260 does not contain lead, but it is a forming grade rather than a free-cutting grade, so it does not machine the way C360 does.
• Where a lead restriction applies to a machined brass part, the grade changes and the machining behaviour changes with it — the finish off the tool steps back and the cycle time lengthens.

Two practical points follow, and both are about timing. Say it at the enquiry stage whether a lead declaration is required, because it decides the grade before anything is quoted. And do not assume the substitute is equivalent — a lead-free brass on a part where the as-machined finish was the finished surface may introduce a secondary operation that was not in the original price.

Some bronze families also contain lead, added for the same reason, so the question applies across the family rather than to brass alone. Where documentation is required with the order, the quality documents page covers what ships and what can be supplied on request.

Dezincification: the failure that starts inside

Brass’s weakness is specific and worth understanding, because it is the reason marine work does not use it.

In certain environments — seawater especially, and particularly where the alloy is high in zinc, the water is warm, the flow is stagnant, or the part is buried in a crevice — the zinc is selectively leached out of the brass. What remains is a porous, copper-rich sponge that looks like the original part from the outside but has lost most of its strength. The part fails suddenly, without visible warning, because the damage happened below the surface.

This is dezincification, and it is why:

• Marine fittings, through-hull components and pump parts are bronze, not brass
• C260, which is higher in copper, resists dezincification better than C360, despite being the less machinable grade
• Stagnant and warm conditions are worse than flowing cold water, which is a design consideration as much as a materials one

Bronze does not have this failure mode. Its corrosion resistance comes from the alloy system as a whole rather than from a zinc content that can be stripped out, and that is why marine hardware has been bronze for as long as it has.

The practical rule for anything that touches seawater: bronze, and design it to drain. A bronze part that traps water in a crevice will still give trouble; a bronze part that drains will outlast the vessel. See the marine parts page for how that plays out on deck hardware and fittings.

Where each one actually lives

Copper shows up as:

• Busbars, terminals and contacts
• Heat sinks and thermal components
• Electrical hardware where conductivity is the function
• Electrodes and current-carrying parts
• Brazed and welded assemblies, where oxygen-free copper is specified

Brass shows up as:

• Fittings, adapters and valve components — see fittings and adapters
• Turned fasteners, nuts and small threaded parts
• Instrument and electrical hardware where moderate conductivity and good machinability are both wanted
• Decorative and architectural parts
• Cold-formed components in C260

Bronze shows up as:

• Bushings, sleeve bearings and wear plates — see bushings and sleeves
• Marine fittings, pump components and valve seats
• Worm wheels and low-load drive components
• Parts that have to run against a steel shaft
• Anything that has to survive seawater

The pattern is clean: conductivity points at copper, machinability and cost point at brass, bearings and seawater point at bronze.

Cost runs the opposite way to what people assume

Per kilo, copper is the most expensive of the three — it has no cheap addition diluting it. Brass is the cheapest, because zinc is inexpensive and makes up a third of the alloy. Bronze sits between and moves with the tin content, which is the expensive element.

On a finished part, though, the ranking can change. A cheap alloy that machines badly can cost more to produce than an expensive alloy that machines well, because the machining cost is a per-part cost that applies to every piece in the batch. That is why a brass fitting is often cheaper as a finished part than the same fitting in copper, despite being a cheaper material to begin with — and why the copper price is only worth paying when conductivity is genuinely the requirement.

For high-volume brass parts, the blank can be forged or headed through our vetted partner network before finish machining, which reduces the material consumed and shortens the machining cycle. The brass and copper parts page covers how that route is quoted.

Three specification mistakes with copper alloys

1. Specifying copper where conductivity is not the requirement. Copper is the most expensive of the three, the worst to machine and the softest. Where a part is a fitting, a bracket, a threaded component or anything that does not carry current or move heat, brass does the job at lower material cost and far lower machining cost. Reaching for copper because it sounds like the premium choice is the most expensive mistake in this comparison.

2. Specifying brass where the part runs as a bearing. Brass will not do what bronze does. A brass bushing running against a steel shaft will gall, pick up material off the shaft and wear quickly, because the alloy has none of the sliding behaviour that the tin and lead in a bearing bronze provide. Where the requirement is a bearing surface, the grade is bronze and the question is which bronze, not whether brass is good enough. This failure is common because the two look similar and both are “copper alloys” on a drawing.

3. Specifying brass for a wet marine or high-chloride part. Dezincification is a slow failure that starts inside the metal, and the part looks sound until it fails. Any brass part in continuous seawater contact should be reconsidered, and the answer is bronze. Where the environment is wet but not saline — fresh water, condensation, washdown — brass performs adequately, and the distinction is worth making explicitly on the drawing because “wet” and “salt water” lead to different alloys.

A fourth, less obvious one: specifying a free-cutting brass for a part that is formed rather than machined. C360 owes its machinability to its lead content, and that same content reduces its ductility. A part that is bent, headed or deep drawn belongs in a forming grade, and forcing a free-cutting brass through a forming operation produces cracks. The two grades are not interchangeable in either direction.

Finishing copper alloys

All three families take plating and coating well, and the finishes commonly specified are the same:

• Nickel plating for a hard, durable, corrosion-resistant surface — common on brass electrical hardware and on parts that see handling
• Tin plating for solderability and a matte, low-tarnish appearance — common on electrical terminals and contacts
• Clear or tinted lacquer to hold a polished appearance without letting the metal patinate, typical on decorative brass
• Chromate conversion and passivation where a specific corrosion or appearance requirement applies
• Polishing and brushing for the finish itself, which many brass and copper parts ship as

Two points matter in practice. First, plating a part with a machined finish underneath shows every tool mark, so where a cosmetic finish is specified the as-machined surface is part of the specification. Second, copper and brass are subject to tarnish and patina if left bare, which is a design decision rather than a defect — some architectural and decorative work relies on it, and parts meant to hold a bright appearance need a lacquer or a plating.

Finishing runs through our vetted partner network, managed under one quality process, and the finish sits on the same drawing as the geometry. Where the appearance matters, it is worth saying so at the quotation stage rather than specifying a finish and discovering that the surface beneath it needed attention too.

The callout that belongs on the drawing

Instead of	Write
Brass	C360 for a machined part; C260 for a formed or deep-drawn part
Brass, RoHS compliant	C360 contains lead — say so and the grade changes
Bronze	Name the family — bearing bronze or aluminium bronze — and the application
Copper	C110 for general conductivity; C101 where brazing, welding or vacuum service is involved
Brass, marine	Revisit — brass dezincifies in seawater; bronze is the marine answer
Copper, machined complex part	Revisit if conductivity is not the requirement — brass machines far better and costs less

Two lines belong on any copper-alloy drawing: the grade, and what the part actually has to do — carry current, run as a bearing, or survive a wet environment. Those two facts decide the alloy more often than any strength figure does.

The families we machine are listed on the materials page. Send the drawing, the grade and the duty, and the quote comes back within 24 hours with DFM feedback — including a note where the alloy and the application are working against each other. Orders start at 50 pieces per style and material, samples from a single piece in 5–10 days, and every batch ships with a material certificate (MTR) tracing the alloy to its mill heat plus pre-shipment photos.