Brass vs Bronze vs Copper: Which Metal for Your Machined Parts?

Brass, bronze, and copper sit next to each other on every material rack, and buyers mix up the names constantly. The difference between brass and bronze comes down to the alloying element. Brass is copper plus zinc — the free-machining C360 grade runs about 61.5% copper, 35.5% zinc, and 3% lead. Bronze is copper plus tin in its classic form, though the engineering family has widened: aluminum bronze (copper-aluminum) and phosphor bronze (copper-tin-phosphorus) are bronzes too. Copper itself, in grades like C110 ETP, is 99.90% pure metal.

That one difference in chemistry cascades into everything a buyer cares about: how fast the part machines, whether it survives seawater, how much current it carries, and what the raw bar costs. There is no universal "best" — but for any given part, there is usually a clear right answer.

Copper alloys are ranked on a machinability scale where C360 free-cutting brass = 100. Its ~3% lead content acts as a built-in chip breaker: chips come off short and clean, tools last, and cycle times drop. That is why C360 dominates high-volume turned fittings, connectors, and threaded components — when the drawing just says "brass," this is usually the grade. For shop-ready grade picks and cutting parameters, see our guide to machining brass.

The bronzes machine well but slower: C932 bearing bronze rates around 70 and C954 aluminum bronze around 60. Respectable numbers — no shop fears bronze — but you pay for the alloy’s extra capability in cycle time. Pure C110 copper rates just 20. It is soft and gummy, produces long stringy chips, and work-hardens at the cut. Copper parts are absolutely machinable — sharp tools, high rake angles, disciplined feeds — but expect longer cycle times and more burr control work. Never specify pure copper when brass would do; you pay more for the material and more for the machining.

For load-bearing and wear duty, the ranking flips. C954 aluminum bronze is the strongest common grade here at 515–620 MPa tensile — nearly double C360 brass (303–372 MPa) and well beyond C110 copper (220–310 MPa by temper). C932 bearing bronze is softer (207–241 MPa) by design: as a bearing material it embeds contaminants and runs against steel shafts without galling, which is why it remains the default bushing and thrust-washer stock a century after SAE 660 was standardized. Brass sits in the middle — stronger than pure copper, no bearing credentials. Gears, wear plates, pump sleeves, valve bodies, and heavy bushings are bronze parts; drawing callouts that say "brass" for these are worth a second look.

All three resist ordinary atmospheric corrosion well — that is the family trait. The differences show up in water. Brass’s zinc is its weak point: in chloride-containing, warm, stagnant, or acidic water, brass can suffer dezincification — zinc selectively leaches out, leaving a porous copper-rich skeleton that looks intact but has lost its strength. Fittings that weep or crumble after years in aggressive water are the classic symptom. None of them rust in the iron-oxide sense; what actually happens to copper over time is covered in does copper rust.

Bronze is the marine answer. Aluminum bronzes like C954 are specified for seawater bearings, pump and valve components, propellers, and marine fasteners precisely because they hold up where brass quietly degrades. Pure copper handles many waters well and develops its familiar protective patina, but for load-bearing marine hardware, bronze is the default engineering choice. Rule of thumb: dry or freshwater service — any of the three; saltwater — bronze.

Material pages with grade-by-grade detail: brass CNC machining, and the wider selection logic in our CNC machining materials guide. For the stainless side of the same decision, see 304 vs 316 stainless steel.