Guide
Which ASTM brass bar specification should a drawing call out for a lead-free or free-cutting turned part?
An ASTM brass bar specification is the numbered standard that tells a mill which alloys, product forms and tempers it may ship against a purchase order, and a drawing that names the wrong one either contradicts itself or lets the supplier choose. For turned brass parts, five specifications are in play: B16 for free-cutting brass, B927 for a list of plain brasses that includes low-lead C27450, B371 for copper-zinc-silicon rod, B453 for other leaded brasses and B124 for forging stock. This guide shows which one fits which part and how to word the material note.
By Saola Manufacturing engineering team · Published · Updated
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What does a brass bar material note have to identify?
It has to identify the alloy by UNS number, the ASTM specification and edition, the product form and the temper, because the specification alone often covers several alloys. A note that says only “brass bar” leaves each of those to the supplier.
The specifications overlap in a way that makes short notes dangerous. ASTM B927 lists more than a dozen alloys in its scope, and ASTM B371 lists eight silicon-brass alloys and says that when the purchaser does not specify the alloy, any alloy listed in its scope may be supplied (see the B927/B927M-23 store page and the B371/B371M-19 store page). Naming the specification without the UNS number therefore does not fix the alloy.
Edition matters too. B927/B927M-17 is now marked historical and B927/B927M-23 is the active edition, and the later scope adds C27550 to the earlier list, per the two ASTM store pages. A drawing that cites a specification without a year should say whether the latest edition applies and who decides when it changes.
The table summarizes which specification covers which alloy family. Read it as a map of scope lines taken from the ASTM store pages, not as a substitute for the standards, which are sold by ASTM.
| Specification | Alloys named in the scope | Use for |
|---|---|---|
| ASTM B16/B16M | C36000, C36010 (free-cutting brass) | Leaded free-cutting brass for screw machining and moderate thread rolling |
| ASTM B927/B927M | C21000 through C28500, including C27450, C27451, C27453, C27550 | Brasses in round, hex, octagonal rod and rectangular, square bar; includes low-lead C27450 |
| ASTM B371/B371M | C69240, C69300, C69400, C69410, C69430, C69700, C69710, C69850 | Copper-zinc-silicon rod, including C69300 |
| ASTM B453/B453M | C33500, C34000, C34500, C35000, C35300, C35330, C35350, C35600 (C36000 is not listed) | Other leaded brasses for parts that need extensive machining before cold forming |
| ASTM B124/B124M | Copper and copper alloys for hot forging, including C37700 | Forging stock, not screw-machine bar |
When is ASTM B16 the right call-out?
Use B16 when the part is a leaded free-cutting brass, C36000 or C36010, and the part is not a drinking-water product that has to be lead free. B16 covers only those two alloys.
The B16/B16M-24 scope covers rod, bar, wire and shapes of any specified cross section in C36000 or C36010, described as suitable for high-speed screw machining and moderate thread rolling. The earlier B16/B16M-19 edition is marked historical on the ASTM store.
Because both alloys are leaded free-cutting brasses, B16 is a contradiction on a drawing that also asks for lead-free material. The legal side of that choice, including which plumbing parts are exempt, is in our guide to the federal lead-free exemptions.
Which specification covers lead-free or low-lead bar: B927 or B371?
B927 is the specification for round, hex and rectangular bar in C27450 and the other brasses it lists, and B371 is the one for silicon-brass rod such as C69300. The choice follows the UNS number you want, not the other way around.
The B927 scope names C27450 and C27451 among its alloys and lists tempers O60, H01, H02 and H04 for rod and bar. The B371 scope lists C69300 and names tempers by alloy: half hard, H02, for C69300 and hard, H04, for the other alloys, per the abstract of the -19 edition. The store listing shows the same edition reapproved in 2026.
B371 is titled rod. If the drawing needs hex or another shape in C69300, confirm with the supplier which specification the mill will ship against, because the store page does not show shape coverage. Put the alloy first on the drawing and add the specification the supplier confirms.
The compliance side of choosing an alloy, including how the lead-free alloys machine, is in our guide to lead-free brass for NSF 61 and NSF 372. This guide stays with the paperwork.
Where do B453 and B124 fit, and why are they not the answer?
B453 is a different leaded brass family that does not include C36000, and B124 is forging rod, so neither is a substitute for B16 or B927 on a screw-machined part. Each is easy to cite by mistake.
The B453/B453M scope lists C33500, C34000, C34500, C35000, C35300 and related leaded brasses, and C36000 is not among them. It suits parts that need extensive machining before cold forming, with tempers O60, H01 and H02. A drawing that says “leaded brass per B453, C36000” is therefore asking for something the specification does not cover.
The B124/B124M-20 scope covers rod, bar and shapes intended for hot forging, in tempers H50, M20 and M30, and includes C37700. It is the right stock for a forged blank, and the wrong one for a part turned directly from bar. The comparison between forged and bar-stock routes is in our guide to hot forging vs bar stock.
What exact words avoid a supplier guess?
Write the UNS number, then the ASTM specification and edition, then the temper, then a ban on substitution. For example: “Material: UNS C27450 per ASTM B927/B927M-23, temper H02, hex rod; no substitution of alloy or specification without written approval.”
For a free-cutting part the same pattern reads “UNS C36000 per ASTM B16/B16M-24”, followed by the temper and form. For a silicon-brass part it reads “UNS C69300 per ASTM B371/B371M-19, temper H02”, adding the shape the mill has confirmed. If the buyer will accept an equivalent, say so in one sentence and name who approves it; otherwise the note should say that none is allowed.
Avoid three phrasings: a trade name in place of a UNS number, “brass per ASTM B16” when lead-free is also requested, and a specification that is silent on the form. Each is a gap a supplier fills with whatever bar is in stock.
How should the mill certificate be checked against the drawing?
Match four lines: the UNS number, the specification and edition, the temper and the lead reading. If any of the four is missing or different, hold the lot until the supplier confirms in writing.
The certificate should name the heat or lot number that is marked on the bar and carried through on the traveler. How a type 3.1 certificate differs from a type 2.2 one is covered in our guide on EN 10204 3.1 vs 2.2; for brass, a 3.1 document that reports the chemistry by heat is the more useful of the two.
Ask the supplier to keep leaded and lead-free bar in separate, labeled stock and to confirm the alloy at the first operation on the CNC turning floor. A wrong-alloy part is almost impossible to spot by eye, and the check is cheap at the start of the run and expensive after shipment.
Frequently asked
Is C27450 covered by B16?
No. B16 covers C36000 and C36010 only. C27450 is listed in the B927 scope.
Can I call out C69300 as ASTM B927?
No. C69300 is listed in the B371 scope, not in B927. Use B371 and confirm the shape the mill will ship.
Does a drawing need the edition year of the ASTM specification?
Yes, or an explicit rule for which edition applies. Editions change: B927 moved from the 2017 edition to the 2023 edition, and the later scope lists an additional alloy.
Is ASTM B453 the same as B16?
No. B453 covers other leaded brasses and does not list C36000, which is the main B16 alloy.
Can I use forging rod to the B124 specification for turned parts?
It is intended for hot forging, so use it only when the part is forged. For turned parts use the bar specification that matches the alloy.
Sources
- ASTM B16/B16M-24, Free-Cutting Brass Rod, Bar and Shapes for Use in Screw Machines, ASTM International, 2024
- ASTM B927/B927M-23, Brass Rod, Bar, and Shapes, ASTM International, 2023 (the 2017 edition is marked historical)
- ASTM B371/B371M-19, Copper-Zinc-Silicon Alloy Rod, ASTM International, 2019, reapproved 2026 per the store listing
- ASTM B453/B453M-19 (R2026), Copper-Zinc-Lead Alloy (Leaded-Brass) Rod, Bar, and Shapes, ASTM International, 2019, reapproved 2026
- ASTM B124/B124M-20, Copper and Copper Alloy Forging Rod, Bar, and Shapes, ASTM International, 2020