Aluminium vs Brass Fittings: When to Switch and When Not To

We get asked this question regularly by engineers who are designing systems and have a choice: aluminium or brass? The honest answer is that both materials are excellent in their respective domains, and the decision becomes clear once you work through five specific variables. Here is the framework.

Variable 1: The Fluid or Gas Being Carried

This is the first filter and it immediately eliminates one material for many applications.

Choose brass when carrying: Potable water (especially with WRAS/NSF certification requirements), natural gas or LPG, low-pressure steam, hydraulic fluid (most types), or any fluid where the fitting must be certified by a third-party body for that specific service.

Choose aluminium when carrying: Dry compressed air, nitrogen, inert gases, clean pneumatic fluid, instrument air. In these services, aluminium is lighter, cheaper, and performs equally or better than brass.

Do not use aluminium with: Strong alkalis (pH >9), hydrochloric and hydrofluoric acid, mercury and mercury compounds, or any fluid that specifically attacks aluminium. Do not use aluminium for plumbing fittings in contact with potable water: aluminium alloys are not on the European positive list of metals for drinking-water contact, and aluminium-bodied fittings are practically absent from the WRAS, NSF/ANSI 61 and WaterMark listings. Do not use aluminium with wet steam.

Variable 2: Weight Sensitivity

Aluminium is roughly one-third the weight of brass per unit volume. If the application is weight-sensitive — mobile equipment, handheld tools, aerospace, automotive, racing — aluminium wins on weight every time. If the fitting is permanently installed in a fixed location, weight is largely irrelevant to the engineering decision.

Variable 3: Corrosion Environment

Variable 4: Pressure and Temperature Requirements

Brass (CW617N, condition R360) has a minimum tensile strength of 360 MPa (EN 12164) and loses strength only gradually up to about 150 °C. Aluminium 6061-T6 has a typical tensile strength of about 310 MPa but — importantly — de-rates far more steeply with temperature than brass.

After long exposure, 6061-T6 keeps roughly three-quarters of its room-temperature tensile strength at 150 °C and well under half at 200 °C, because the precipitation-hardened temper over-ages. Brass has no such temper to lose; its limit is set by gradual softening, creep and the seals.

For applications with continuous elevated temperature service, check the aluminium alloy's temperature-strength curve before specifying. For standard compressed air or pneumatics at ambient to 60°C, this is not a concern.

Variable 5: Certification Requirements

This is the variable that often makes the decision for you: regulated applications require certified fittings, and the available certifications differ significantly between materials.

Approvals that exist for finished brass products: WRAS (UK potable water), NSF/ANSI 61 (USA potable water), NSF/ANSI 372 (lead-free), WaterMark (Australia), DVGW (Germany gas), CE (EU pressure equipment), UL/FM (fire suppression), and many others.

For aluminium products: CE (pressure equipment for industrial use) and specific aerospace standards. Notably absent: WRAS, NSF, WaterMark for potable water. Potable-water approvals for aluminium plumbing fittings are practically non-existent.

If your application requires a specific third-party product certification, identify that requirement first and let it determine your material. No amount of engineering argument will substitute for a missing regulatory approval.

The Cost Comparison — Done Honestly

Aluminium costs less per kilogram than brass, and because it has one-third of the density, the same part needs only a third of the weight of metal. CNC machining of aluminium is fast. The unit price of an aluminium fitting is therefore usually noticeably lower than that of a brass fitting of the same geometry — although brass swarf has a high scrap value, which narrows the gap on heavily machined parts.

But this comparison ignores total system cost. If the aluminium fitting requires anodising for corrosion protection, add that cost. If it requires dielectric isolation from adjacent copper or steel components, add that cost. If it has a shorter service life in a marginal environment and needs earlier replacement, add that cost.

The honest cost comparison is total cost of ownership over the system design life — not just unit price. In many applications, aluminium's lower unit price plus appropriate surface treatment equals or beats brass on total cost. In applications where brass's superior corrosion resistance eliminates surface treatment needs and maintenance replacements, brass can be the better total cost option despite higher unit price.

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Last reviewed: September 2026. Standards and regulatory references are checked at each review.