Brass or copper? Start with the job, not the alloy name
Engineers often write “brass” or “copper” on a drawing when they mean very different performance. Free-machining brass such as C360 is chosen because chips break cleanly and CNC cycle times stay short. Electrolytic tough pitch copper such as C110 is chosen for electrical and thermal conductivity that brass cannot match. Mixing the two labels leads to wrong quotes, wrong plating notes and parts that machine poorly or conduct poorly.
This article contrasts common machined brass and copper choices—especially C360-class free-machining brass versus C110 copper—so you can pick the alloy that matches conductivity, strength, cosmetics and manufacturability.
What “brass” and “copper” usually mean on RFQs
Free-machining brass (C360 family)
C360 brass (often called free-cutting brass) is a copper-zinc alloy with a small lead addition that promotes short chips. It is the default for turned fittings, valve components, connectors and decorative hardware that must machine quickly. Strength is moderate; corrosion resistance in many indoor and mild outdoor settings is good; electrical conductivity is far below pure copper.
C110 copper (ETP copper)
C110 is commercially pure copper with excellent electrical and thermal conductivity. It is soft relative to steels and to many brasses in the half-hard or harder tempers used for machining. Chips are stringy. Tools smear if feeds and clearances are wrong. Designers specify C110 when conductivity, solderability or copper’s distinctive appearance matter more than easy machining. Other brasses (C260 cartridge brass, silicon brasses, naval brasses) and other coppers (C101/C102 oxygen-free, tellurium copper C145 for improved machinability) appear in specialized work. If your drawing only says “brass” or “copper,” expect a clarifying question—or a shop default that may not match your intent.
Property comparison that drives selection
| Property (typical handbook class) | C360 brass (free-machining) | C110 copper |
|---|---|---|
| Electrical conductivity | Much lower than pure copper | Excellent (ETP copper class) |
| Thermal conductivity | Moderate for copper alloys | Excellent |
| Machinability | Excellent; short chips | Fair to poor; stringy chips |
| Strength / hardness (common tempers) | Higher than soft copper for many turned parts | Soft unless cold-worked; yields easily |
| Corrosion in mild atmospheres | Generally good | Good; tarnishes; may need coating |
| Magnetic behavior | Non-magnetic | Non-magnetic |
| Relative material cost tendency | Often lower than high-conductivity copper forms | Copper premium when conductivity is required |
| Cosmetic color | Yellow / gold family | Red / copper family |
Values vary with temper and exact composition. Design to the certificate for purchased stock, not to a brochure average, when conductivity or strength is contractual.
When C360-class brass is the better machined choice
Pick free-machining brass when:
- The part is dominated by turning, milling or Swiss machining and you need predictable short chips
- Electrical conductivity is not a primary requirement (or a plated contact strategy handles the interface)
- You need better strength and dent resistance than soft copper for threaded fittings and small structural bits
- Decorative gold-like appearance is desired, possibly with clear coat or plating later
- Valve, fitting, instrumentation and connector-style geometries are the norm
Brass threads, knurls and fine Swiss features generally behave well. Lead-containing free-cutting brasses have regulatory and end-use restrictions in some potable-water and certain market contexts—confirm the alloy is acceptable for the product’s regulations before locking C360.
When C110 copper is worth the machining pain
Pick C110 (or a closely related high-conductivity copper) when:
- Bus bars, high-current terminals, heat spreaders or RF/thermal paths need copper-level conductivity
- Soft soldering and high conductivity to mating copper are required
- The visual or functional requirement is truly copper, not brass-colored
- Cross-section and length are set by ampacity or heat flow rather than by mechanical load alone
Plan for slower machining, sharp polished tooling, adequate coolant and possibly a more machinable copper alloy (such as tellurium copper) if the geometry is filled with tiny features and conductivity can tolerate a small tradeoff. Tellurium copper is still copper-rich and machines more like a free-cutting alloy than C110 does.
Machining and design implications
Chip control and tool life
Brass C360: high speeds, short chips, excellent surface potential on turned diameters. Copper C110: lower effective productivity, risk of built-up edge, long chips that wrap. Programmed chip breaks, careful rake geometry and secure workholding matter more.
Tolerances and stiffness
Soft copper deflects and galls. Thin copper walls and slender stems need generous fillets, shorter stick-out and inspection plans that do not crush the part. Brass holds size more willingly on small CNC features.
Threads and tapped holes
Both alloys tap, but copper smears more. Prefer rolled or carefully cut threads with sharp taps and proper engagement length. Call out thread class realistically; ultra-fine cosmetic threads on soft copper invite scrap.
Workholding marks
Copper shows vise and chuck marks readily. Protect cosmetic faces, or machine them last, or specify a finish that hides handling (bead blast is uncommon on copper cosmetics; brushing or plating is more typical).
Joining, plating and finishing notes
- Soldering: both can solder; copper is often chosen specifically because joints and conductivity align
- Brazing: common on copper fluid and electrical assemblies; watch temper loss in the heat-affected zone
- Plating: nickel, tin and other platings appear on both for corrosion, solderability or wear; call out masking of electrical contact zones
- Passivation-style stainless processes do not apply; copper alloys use cleaning, bright dips or coatings appropriate to copper metals
- Clear coats and lacquers sometimes preserve brass or copper color on decorative parts
If conductivity through a plated stack matters, specify plating thickness limits and test methods—or keep contact lands bare as designed.
Drawing and RFQ checklist
1. State the exact UNS or common alloy (for example C36000 / C360, or C11000 / C110), not only “brass” or “copper”
2. Call out temper or hardness when strength or formability matters
3. Mark electrical or thermal critical faces and any plating keep-out zones
4. Note regulatory constraints (drinking water, RoHS-related customer rules, lead-free requirements) that may forbid standard free-cutting brass
5. For copper, indicate whether tellurium copper or another free-machining copper is an allowed alternate
6. Provide finish expectations: as-machined, brushed, plated, lacquered
7. Avoid copying steel tolerances onto soft copper stems without checking deflection
Decision flow in plain language
If the part must carry current or heat like copper, start with C110 or another high-conductivity copper and accept machining cost—or switch to a free-machining copper only after conductivity math still passes.
If the part is a machined fitting, knob, manifold detail or decorative hardware without copper-level conductivity needs, start with C360-class brass (or a regulation-compliant brass alternative) and machine it efficiently.
If you need both high conductivity and aggressive small-feature machining, discuss tellurium copper or a hybrid design (copper conductor + brass mechanical shell) before freezing a single alloy.
Mistakes that show up in incoming drawings
- Labeling a bus bar “brass” because the CAD library default was yellow
- Specifying C110 for a dense Swiss-turned connector body that will not hold schedule
- Omitting temper, then rejecting parts for softness or for springiness
- Plating notes copied from steel drawings that do not fit copper alloys
- Tight positional tolerances on slender copper pins without a datum scheme that matches inspection force
- Assuming all “brass” is lead-free and potable-water safe
Summary for buyers and design reviewers
C360-class brass is the machinability champion in the copper-alloy family for general CNC and Swiss work. C110 copper is the conductivity champion and a machining challenge. Write the alloy and the functional reason on the drawing. When in doubt, separate the electrical path from the mechanical housing in the design instead of forcing one metal to do both jobs poorly.
For a quote, send alloy + temper, a clear model, plating or finish notes, and whether conductivity is contractual. That single package prevents the most common brass/copper clarification delays.