Brass CNC machining is the fastest way to produce precision metal parts that also have to look good, carry current or survive a threaded fitting. Brass is the reference material against which every other metal's machinability is rated: free-cutting brass C36000 is defined as 100% machinability, and everything else — aluminium, steel, titanium — is measured against it. That has a direct consequence for buyers: brass parts machine faster, hold finer detail, and often cost less per part than aluminium despite costing more per kilogram. This guide covers the grades you will actually be quoted, realistic tolerances, where brass genuinely outperforms aluminium and stainless, where it does not, and the finishing and compliance points that catch buyers out.
Why Brass Machines So Well
Brass is a copper-zinc alloy, and the grades used for machining contain a small amount of lead, which acts as a chip breaker and a lubricant at the cutting edge. The result is short, clean chips, low cutting forces, excellent surface finish straight off the tool and very long tool life.
Practically, that means:
- Cutting speeds roughly 1.3x those of aluminium and 4x those of stainless.
- Tool life around 1.5x aluminium and 4x stainless on comparable geometry.
- Machining cost per part typically 15% to 25% below aluminium, despite brass stock costing more per kilogram.
- Fine features — small threads, knurls, engraved detail, thin webs — hold their edges without the burr and tear-out you get in softer alloys.
Brass Grades You Will Actually Be Quoted
| Grade | Common name | Composition | Machinability | Typical use |
|---|---|---|---|---|
| C36000 / C3604 | Free-cutting brass | Cu 61.5%, Zn 35.5%, Pb 3% | 100% (reference) | Turned parts, fittings, inserts, fasteners |
| C37700 | Forging brass | Cu 59%, Zn 39%, Pb 2% | 90% | Hot-formed then machined components |
| C26000 | Cartridge brass | Cu 70%, Zn 30% | 30% | Deep-drawn parts, decorative trim |
| C46400 | Naval brass | Cu 59%, Zn 40%, Sn 1% | 30% | Marine hardware, seawater-exposed parts |
| C23000 / H62 | Red brass / common brass | Cu 62-85%, Zn balance | 30-40% | Plumbing, architectural, general hardware |
| C69300 / lead-free | EnviroBrass style | Cu-Zn-Si, Pb below 0.1% | 70-80% | Potable water and RoHS-tight applications |
If a drawing simply says "brass", ask which grade. The machinability spread between C360 and C260 is more than threefold, and it shows up directly in the quote.
370 Brass Machining: The Free-Cutting Workhorse
370 brass machining centres on UNS C37000, a free-cutting brass at roughly Cu 60%, Zn 39% and Pb 1%. The reduced lead content — about a third of C36000 — is the whole point: enough lead remains at the cutting edge to break chips short and keep tool life long, while the alloy stays forgeable. That makes 370 the natural choice when a part is hot-forged or extruded to near-net shape and then finished on a turning centre or Swiss lathe.
In practice 370 brass machining runs at a machinability rating of around 70 against the C36000 = 100 baseline. Expect:
- Tensile strength in the 310 to 435 MPa range depending on section size and temper, with elongation around 18% to 45%.
- Cutting speeds roughly 10% to 20% below C360 — still far ahead of any steel or stainless.
- Clean thread and knurl quality on fittings, valve bodies, couplings and architectural hardware.
If your drawing calls for 370 brass, specify the temper as well. Half-hard drawn stock behaves differently from as-extruded bar, and the difference shows up in surface finish and in how thin a wall you can hold without chatter.
443 Brass Machining: When Corrosion Outranks Chip Control
443 brass machining is a different proposition. UNS C44300 — Admiralty brass, sometimes called arsenical brass — runs Cu 70-73% with Sn 0.9-1.2% and a trace of arsenic, and it is specified for corrosion resistance first and machinability second. The tin exists to stop dezincification, the process where zinc leaches out of the alloy in seawater and leaves a weak, porous copper structure behind.
The trade-off is explicit: C44300 carries a machinability rating of 30 on the same C36000 = 100 baseline. That is roughly a third of free-cutting brass, and it shows up in the quote:
- Cutting speeds drop substantially and tool wear rises, so cycle time per part is materially longer than on 370 or C360.
- Chips run stringier. Specify chip breakers and plan for more frequent tool changes on long runs.
- It is most often supplied as tube and plate rather than bar, so parts are frequently machined from tubular stock instead of solid.
Specify 443 brass machining when the part lives in seawater, brackish water, or a heat exchanger or condenser circuit — Bourdon tubes, ferrules, evaporator and distiller tubes, pump liners. Do not specify it for a high-volume turned fitting that never touches anything corrosive; you will be paying for corrosion resistance you never use.
370 Low Lead Brass Machining: RoHS and Potable Water
370 low lead brass machining addresses the compliance question that sits behind every brass RFQ. Standard free-cutting brasses rely on lead for chip control, but lead is restricted under RoHS and under potable-water rules such as NSF/ANSI 372 and the EU Drinking Water Directive. Low-lead 370 variants — and the closely related C37700 forging brass — cut lead to a level that clears those rules while keeping the alloy forgeable and machinable enough to finish.
What to expect on the shop floor:
- Machinability sits below standard C360 but above the tin brasses — workable on Swiss and screw machines with adjusted parameters.
- Forging behaviour stays good, so the near-net-shape route that makes 370 economical is still open.
- Corrosion resistance improves as lead drops, which matters for plumbing and outdoor hardware.
If your market is the EU, or the part touches drinking water, say so in the RFQ and ask for the alloy certificate. A drawing that only says “brass” will be quoted in C360 — and C360 will fail the lead test.
Tolerances and Surface Finish
Brass is dimensionally stable and cuts cleanly, which makes it one of the easiest materials to hold tight tolerances in. Our standard capability is ±0.01 mm, and on brass turned and milled features that figure is comfortably repeatable across a production run rather than a first-article achievement. Fine threads, small-diameter bores and knurled surfaces are where brass shows the biggest advantage over aluminium.
As-machined surface finish lands around Ra 0.8 to 1.6 µm without a dedicated finishing pass, which is better than aluminium typically achieves in the same operation. Full tolerance guidance is in CNC machining tolerances.
Where Brass Genuinely Wins
Electrical contacts and terminals. Brass carries current reasonably well — around 26% IACS for C360 versus 100% for pure copper — while machining far more cleanly than copper. That combination is why connector bodies, terminal posts and contact carriers are so often brass. See electroacoustic components for the audio-side equivalents.
Threaded fittings, valves and plumbing. Brass threads machine crisply, gall less than stainless, and seal well. Valve bodies, hose fittings and compression components are classic brass work.
Decorative and audio trim. Polished or brushed brass has a warmth that anodised aluminium cannot imitate, which is why knobs, escutcheons, trim rings and badges are specified in brass when the brand wants a particular look. See audio knobs.
Small precision turned parts. Inserts, spacers, standoffs, custom nuts and studs and general precision fasteners run faster and cleaner in brass than in stainless, with less tool wear per thousand pieces.
Wear surfaces and low-load gears. Brass runs against steel with low friction and does not seize, which suits small gears, bushings and ratchet components.
Where Brass Loses
- Weight. At roughly 8.5 g/cm³, brass is about 3.1x heavier than aluminium. Any weight-constrained design — UAV structure, portable devices, moving robotics axes — should not be brass.
- Strength. C360 yield strength sits around 125 to 310 MPa depending on temper, well below 6061-T6 and far below 7075-T6 or alloy steel.
- Material cost. Brass stock typically costs 1.5x to 2.5x aluminium by weight, and copper price volatility feeds straight through.
- Dezincification. Alloys above about 15% zinc can leach zinc in certain water chemistries, leaving a porous copper structure. Naval brass or inhibited grades solve it; standard free-cutting brass does not.
- Stress corrosion cracking. Brass under sustained tensile stress in an ammoniacal environment will crack. If your part sees that, specify a resistant grade or a different alloy.
- Tarnish. Uncoated brass darkens. If the part is decorative and will be handled, it needs a lacquer or plating.
Finishing Brass
| Finish | What it does | Notes |
|---|---|---|
| Polishing / buffing | Mirror or satin appearance | Needs a lacquer afterwards or it will tarnish |
| Clear lacquer | Locks in the polished look | Adds a thin film — check it does not affect fits |
| Nickel or chrome plating | Wear resistance, brighter finish | Adds measurable thickness; mask critical threads |
| Tin plating | Solderability, food-contact friendly | Common on electrical parts |
| Passivation / anti-tarnish dip | Slows oxidation without changing dimensions | Good for parts that must stay bare |
| Brushing | Directional satin grain | Popular on audio trim |
If a finish adds thickness, say which features must be masked. The same rule that applies to anodizing aluminum applies here: dimensional responsibility has to sit with one party.
Brass vs Aluminium vs Stainless
| Factor | Brass C360 | Aluminium 6061 | Stainless 303/304 |
|---|---|---|---|
| Machinability rating | 100% (reference) | 90% | 45% |
| Relative machining cost | -15% to -25% vs Al | Baseline | +80% to +120% vs Al |
| Density | 8.5 g/cm³ | 2.7 g/cm³ | 8.0 g/cm³ |
| Electrical conductivity | ~26% IACS | ~40% IACS | ~2.5% IACS |
| Corrosion behaviour | Good, watch dezincification | Good, best anodised | Excellent |
| Lead content | 2.5-3.7% (C360) | None | None |
| Best for | Fittings, contacts, trim, fasteners | Structural, lightweight, enclosures | Medical, food, marine, high strength |
Compliance Note: Lead and RoHS
Free-cutting brass C360 contains roughly 2.5% to 3.7% lead. Copper alloys are covered by a RoHS exemption allowing up to 4% lead by weight, so C360 remains compliant for most EU electronic and electrical applications — but the exemption is reviewed periodically, and some customers impose their own internal limits regardless. If your product needs to be demonstrably lead-free, specify a lead-free grade such as C69300 or a silicon brass at the RFQ stage, not after the first article is approved.
Design and Sourcing Tips
- Specify the grade, not just "brass". The machinability and cost spread is too large to leave open.
- Exploit the machinability. Fine threads and small features that would be marginal in stainless are routine in brass — design to that capability.
- Watch the weight. If the part moves or is carried, run the mass calculation before committing.
- Decide the finish early. A lacquer or plating step changes both dimensions and lead time.
- Consider stamping for flat parts. Thin flat brass components are often cheaper as precision stampings once volume justifies a die.
- Ask for material certs. Copper alloy composition varies more between mills than aluminium does.
A brass CNC machining programme rewards early decisions, because grade, finish and lead-content requirements are all cheaper to settle before the first article than after it.
More on material selection generally is in CNC machining materials, with dedicated comparisons for aluminium and stainless steel. Our CNC milling service handles prismatic brass work and turning handles the rotational parts — see CNC turning service for the full turned-part capability.
Bottom Line
Choose brass CNC machining when the part needs fine machined detail, good electrical or thermal behaviour, a warm finished appearance, or clean threads in a fitting — and when weight and ultimate strength are not the binding constraints. Choose aluminium when mass matters and stainless when strength, corrosion or biocompatibility does.
We run brass CNC machining across turning and milling, with in-house polishing, plating and lacquer, at ±0.01 mm standard and 24-hour quotes on complete RFQ packages.
Send a STEP file and a drawing with the grade specified to gongtianbao@xhlmarketing.com or WhatsApp +86 17620300785.
FAQ: Brass Grades and Machining
What is the difference between 370 brass and 360 brass?
370 brass (UNS C37000) carries roughly 1% lead against about 3% in C36000. That drops machinability from the 100 baseline to around 70, but keeps the alloy forgeable, which C360 is not. Choose 370 when the part is forged or extruded first and machined afterwards.
Is 443 brass easy to machine?
No. 443 brass (UNS C44300, Admiralty brass) has a machinability rating of 30 against C36000 = 100 — about a third of free-cutting brass. It is specified for dezincification and seawater corrosion resistance, and you accept slower cycle times and higher tool wear to get it.
Which brass grade should I choose for a RoHS or potable water part?
Specify a low-lead grade — 370 low lead brass or a lead-free envirobrass — and ask for the alloy certificate with the shipment. Standard C360 will fail a lead-content test under RoHS and NSF/ANSI 372.
What tolerance do you hold on brass parts?
±0.01 mm is our standard capability, and on brass turned and milled features it is comfortably repeatable across a production run rather than a first-article achievement.
What are the grades of brass?
Brass grades sort into four practical families: free-cutting leaded brasses such as C36000, which set the machinability baseline at 100; lower-lead forging and extrusion brasses such as C37000 at roughly 70, chosen when the part is formed first and machined afterwards; dezincification-resistant admiralty brasses such as C44300 at about 30, specified for seawater and corrosion duty; and low-lead or lead-free envirobrass grades for RoHS and potable water work. Most quotes you receive will name one grade from each family rather than every grade in the standard.