BRASS GRADES EXPLAINED

The Unified Numbering System — UNS for short — is the official naming registry for copper alloys, maintained through the Copper Development Association. Every copper alloy gets a designation: a C, followed by five digits. The C just means "copper alloy." The digits after it sort the alloys into families: the C20000 to C49999 range is wrought copper-zinc brasses, and the C80000 to C89999 range is cast copper alloys. That is how C83600 can be a brass even though it starts with an 8 — it is a cast brass.

Here is the honest part most catalogs skip: the digits themselves do not spell out the recipe. You cannot read "C36000" and derive 61.5% copper from it. What the numbers give you is a unique, standardized identity — one grade, one composition range, one set of properties — and the registry publishes the official ranges so nobody has to guess. This page lists the six brass grades that matter, with their real UNS composition ranges and nominal values.

A note on how I state numbers: "nominal" means the target recipe the mill aims for; the range means what the standard allows. I give both, because both are real.

C36000 — Free-Cutting Brass (the machinist's brass). Copper 60.0–63.0% (61.5 nominal), lead 2.5–3.7%, zinc the remainder (~35.5 nominal). The lead is the whole point: it makes chips break off cleanly, so the metal cuts fast on automatic screw machines. It rates 100 on the machinability scale — the standard every other copper alloy is judged against. Fittings, gears, valve stems, and every small brass part a screw machine ever made.

C26000 — Cartridge Brass, 70% (the ammo brass). Copper 68.5–71.5% (70.0 nominal), zinc the remainder (~30.0 nominal). Ductile, deep-draws without cracking, and holds its shape under pressure — the three things a shell case needs. Lamp parts, hinges, and springs use it too, but the name tells you its main stage.

C28000 — Muntz Metal, 60% (the hot-working brass). Copper 59.0–63.0% (60 nominal), zinc the remainder (~40). An alpha-beta brass: strong, hot-workable, and the alloy that loves being extruded into architectural panels, bolts, brazing rod, and condenser plates.

C46400 — Naval Brass (the saltwater brass). Copper 59.0–62.0% (60.0 nominal), tin 0.50–1.00% (0.7 nominal), zinc the remainder (~39.2 nominal). The one percent tin is doing the heavy lifting: it gives the alloy resistance to seawater corrosion and to dezincification. Propellers, seacocks, marine hardware, valve stems — anything that lives in saltwater.

C23000 — Red Brass, 85% (the near-bronze). Copper 84.0–86.0% (85 nominal), zinc the remainder (~15). Pinkish-red, soft, easy to work — and chemically so close to bronze that the naming argument never ends. Plumbing tube, ornamental work, and fittings.

C83600 — Leaded Red Brass (the valve brass, cast). Copper 84.00–86.00%, tin 4.00–6.00%, lead 4.00–6.00%, zinc 4.00–6.00% — the "85-5-5-5" the trade calls it. A cast alloy for valves, fittings, pumps, and plumbing goods. The lead makes it cast cleanly and machine easily; it is the alloy inside half the old valves in America.

That is the whole cast of characters. When you see a C-number on a fitting or a mill certificate, you can come back to this page and know exactly which recipe you are holding. And if you want the bedrock — what brass is in the first place — start there.

The C-numbers are the clean naming system. The trade names are not. "Red brass" (C23000 and C83600) is chemically closer to bronze than to yellow brass, which is why old-timers call red-brass valves "bronze" and are not entirely wrong. "Architectural bronze" (C38500) is, despite the name, actually a brass — the catalog named it for the look, not the chemistry. "Commercial bronze" (C22000) is also a brass: 90% copper, 10% zinc, no tin anywhere near it.

Nobody designed this on purpose. Two centuries of catalogs, foundries, and job sites named things by look and habit, and the names stuck. The honest rule: when the trade name sounds like bronze, check the C-number. The C-number is the one naming system that does not lie. Our brass-vs-bronze guide goes through the full naming mess with the test kit to go with it.