Brass metal is mainly made of copper and zinc, but real engineering brass is rarely just a simple 70/30 mixture. Different brass grades may also contain small amounts of lead, tin, aluminum, manganese, silicon, iron, or nickel to improve machinability, strength, corrosion resistance, hot forging behavior, or dezincification resistance.
This matters for CNC machining and production purchasing because “brass” is not a complete material callout. A free-machining brass used for turned fittings behaves very differently from naval brass, cartridge brass, lead-free brass, or high-strength manganese brass. The wrong brass grade can change cutting performance, thread quality, surface finish, corrosion behavior, regulatory compliance, and part cost.
Quick Answer
Brass is made primarily from copper and zinc. Many common brasses contain about 60-70% copper and 30-40% zinc, but the exact composition depends on the grade. Lead may be added for easier machining, tin for marine corrosion resistance, aluminum or manganese for higher strength, and silicon or bismuth for lead-free machining grades. For precision parts, the question is not only what brass is made of, but which brass grade fits the drawing, environment, machining process, and compliance requirement.
Basic Brass Composition
The two base elements are copper and zinc. Copper gives brass its ductility, corrosion resistance, electrical and thermal conductivity, and warm yellow color. Zinc increases strength and hardness and lowers material cost compared with pure copper. As zinc content increases, brass generally becomes stronger and less copper-colored, but formability and corrosion behavior can change.
| Element | Typical Role in Brass | Engineering Note |
|---|---|---|
| Copper | Main base metal; improves ductility, conductivity, corrosion resistance, and color | Higher copper content usually improves formability and corrosion behavior |
| Zinc | Main alloying element; increases strength and hardness | Too much zinc can increase dezincification risk in some environments |
| Lead | Improves machinability and chip breaking | May be restricted by drinking water, RoHS, or customer compliance rules |
| Tin | Improves resistance in seawater and marine atmospheres | Often seen in naval brass-type alloys |
| Aluminum | Improves strength and corrosion resistance in some grades | Can change machining behavior and finish response |
| Silicon | Used in some lead-free machining brasses | Good alternative when lead is restricted, but not identical to C360 |
The common online statement that brass is “70% copper and 30% zinc” is only a simplified example. Some brass grades are close to that. Many production brass parts are not.
Common Brass Grades and What They Are Made Of
The table below gives practical composition ranges and use cases. Exact limits depend on the standard and product form, so released drawings should reference the correct material specification.
| Brass Grade | Typical Composition Idea | Common Use | DAXIN Review Point |
|---|---|---|---|
| C260 cartridge brass | About 70% copper, 30% zinc | Sheet, formed parts, springs, terminals, drawn parts | Good formability, not the same machining behavior as free-cutting brass |
| C360 free-cutting brass | Copper-zinc with lead added | CNC turned parts, fittings, inserts, threaded components | Excellent machinability, but lead compliance must be checked |
| C353 clock brass | Leaded brass for machining | Small precision machined components | Good chip control, but grade availability may vary |
| C464 naval brass | Copper-zinc with tin | Marine hardware, shafts, fittings, corrosion-prone parts | Better marine resistance than ordinary brass, but not immune to all corrosion |
| C377 forging brass | Lead-containing brass suited to hot forging | Valves, fittings, forged shapes | Forging route matters; not chosen only by chemistry |
| C693 lead-free brass | Copper-zinc-silicon family | Lead-free fittings and machined parts | Useful for compliance, but feeds/speeds and tool wear differ from C360 |
Engineering review note: these are practical summaries, not a substitute for certified material requirements. If the part needs food-contact, drinking-water, RoHS, REACH, marine, electrical, or pressure-related compliance, the drawing should specify the exact grade and standard rather than “brass.”
Why Lead Is Added to Some Brass
Lead is added to many free-machining brass grades because it helps chips break cleanly and reduces tool load. For CNC turning, this can mean faster cycle time, smoother finish, cleaner threads, better small-hole machining, and less burr formation. This is why C360 brass is popular for precision turned fittings, inserts, bushings, nuts, and small connectors.
But lead is also the reason material selection can become complicated. A part used in potable water, electronics, medical-related equipment, consumer products, or export-controlled markets may need a low-lead or lead-free brass. Replacing C360 with a lead-free brass is not always plug-and-play. The new material may have different tool wear, chip shape, surface finish, strength, cost, and availability.
Brass vs Bronze: The Composition Difference
Brass is mainly copper plus zinc. Bronze is mainly copper plus tin, although many modern bronzes include aluminum, silicon, phosphorus, or other elements. This distinction matters because buyers sometimes use brass and bronze loosely based on color.
| Material Family | Main Alloying Element | Typical Strength | Typical Use Difference |
|---|---|---|---|
| Brass | Zinc | Good machinability and general corrosion resistance | Fittings, fasteners, electrical parts, decorative hardware, turned components |
| Bronze | Tin or other non-zinc elements | Often better wear resistance in bearing applications | Bushings, bearings, marine parts, wear plates, heavy-duty sliding components |
For a deeper comparison, see DAXIN’s brass vs bronze guide. If a part is a bushing or bearing surface, “yellow metal” is not enough information. The actual alloy family controls wear behavior.
How Brass Composition Changes Machining
Brass is often called easy to machine, but that statement mainly applies to the right brass grade. Free-machining brass cuts very differently from cartridge brass sheet or lead-free silicon brass. DAXIN reviews brass composition before quoting tight threads, small holes, thin walls, knurling, press-fit features, or cosmetic turned surfaces.
| Composition Change | Machining Effect | Production Risk |
|---|---|---|
| Lead added | Improves chip breaking and tool life | Compliance restrictions may block use |
| Higher zinc | Can increase hardness and strength | May affect forming and corrosion behavior |
| Tin added | Improves marine corrosion resistance | May not machine exactly like C360 |
| Silicon added | Used for some lead-free machining grades | Tooling and chip control may need adjustment |
| Wrong stock form | Bar, plate, tube, forging, and casting behave differently | Same grade name may not guarantee same process result |
For high-volume turned parts, material grade can change cycle time enough to affect unit price. For a one-off prototype, the difference may be small. For thousands of fittings or inserts, choosing a grade with poor chip control can raise cost quickly.
Corrosion and Dezincification
Brass has useful corrosion resistance in many indoor and mild environments, but it is not immune to corrosion. One important failure mode is dezincification, where zinc is selectively removed from the alloy in certain water or chloride-containing environments. The remaining copper-rich structure may look pinkish, porous, weak, or rough.
Dezincification risk depends on water chemistry, temperature, chloride level, oxygen, pH, alloy composition, and service time. This is why plumbing, marine, and valve applications should not use a random brass grade just because it machines well. Dezincification-resistant or application-specific brass may be required.
Electrical and Thermal Conductivity
Brass is less conductive than pure copper, but it is easier to machine, stronger, and often more economical. This makes it useful for terminals, connector bodies, grounding components, cable glands, and electrical hardware where strength, corrosion resistance, thread quality, and conductivity must be balanced.
If maximum conductivity is the priority, copper may be better. If the part needs threads, wear resistance, stiffness, or lower cost, brass may be the more practical choice. The drawing should not simply say “conductive brass” without defining the required electrical performance if that value matters.
Surface Finish and Appearance
Brass color changes with composition. Higher copper brasses can look warmer or more reddish. Higher zinc brasses may appear lighter yellow. Surface finish also matters: polished brass, brushed brass, bead-blasted brass, plated brass, passivated brass, and naturally aged brass can look very different.
Brass can tarnish over time. If the customer wants a stable decorative appearance, a coating, lacquer, plating, or controlled finish may be required. If the part is functional and hidden inside an assembly, appearance variation may be acceptable as long as dimensions and performance are correct.
How DAXIN Reviews Brass Material Requirements
When DAXIN reviews a brass part, we do not treat “brass” as enough information. The manufacturing risk depends on the exact alloy and stock form. A turned connector, a forged valve fitting, a sheet terminal, and a marine bushing may all be brass-related parts, but they do not ask for the same composition.
| Review Item | What We Check | Why It Matters |
|---|---|---|
| Grade callout | C360, C260, C464, C377, C693, or customer-specific standard | “Brass” alone is too vague for production |
| Compliance | Lead-free, RoHS, REACH, drinking-water, food-contact, or customer restrictions | Lead-containing free-machining brass may not be allowed |
| Manufacturing route | CNC turning, milling, forging, stamping, bending, casting, or assembly | Composition and stock form should match the process |
| Critical features | Threads, small holes, knurling, press fits, sealing faces, thin walls | Machinability and burr behavior affect final quality |
| Environment | Indoor, marine, water contact, chemicals, temperature, wear | Corrosion and dezincification risk change grade selection |
| Finish requirement | Raw brass, polished, plated, lacquered, brushed, or aged appearance | Composition and surface prep affect color and finish consistency |
What to Put on a Drawing
A useful drawing should specify more than “brass.” Better notes define the grade, standard, stock form if important, finish, compliance requirement, and any material certificate requirement. For example:
Material: C36000 free-cutting brass bar, ASTM B16, RoHS exemption to be confirmed by customer. Finish: machined, deburred, no plating.
For lead-free work, the note may instead require a specific lead-free grade and certificate. If the part contacts water, food, electronics, or regulated consumer products, material compliance should be discussed before machining, not after parts are finished.
Common Mistakes
| Mistake | Why It Causes Problems | Better Practice |
|---|---|---|
| Writing only “brass” on the drawing | Supplier may choose a grade that machines well but fails compliance or corrosion needs | Specify alloy grade and standard |
| Assuming all brass is 70/30 | Many machined brass parts use leaded or special grades | Match composition to function |
| Replacing C360 with lead-free brass without review | Machining, burrs, tool wear, and cost can change | Validate process and tolerance risk |
| Using free-machining brass in water service blindly | Dezincification or lead compliance may be unacceptable | Review environment and regulations |
| Choosing by color only | Color does not define strength, wear, or corrosion behavior | Use material data and application requirements |
| Ignoring stock form | Bar, sheet, forging, and casting are not interchangeable | Specify product form when it affects performance |
Related DAXIN Services
DAXIN supports CNC machining, turning, milling, threading, knurling, deburring, surface finishing, and material review for brass, bronze, copper, aluminum, stainless steel, titanium, plastics, and nickel alloys. Related resources include brass vs bronze, yield strength vs tensile strength, surface finish chart, and CNC machining for automotive parts.
CTA
Need brass CNC parts with the right grade, clean threads, stable finish, and realistic compliance review? Upload Your CAD File / Get a Quote. DAXIN can review brass composition, machinability, lead-free requirements, corrosion risk, tolerances, and finishing requirements before production.