Choosing the Right Fitting Material: Plastic, Brass, or Stainless?

When you’re building or maintaining a fluid or air system, choosing the right fitting material is just as important as choosing the right tubing. And while John Guest push-to-connect fittings have become a go-to for many applications—thanks to their reliability and ease of use—it’s worth digging deeper into what different materials offer.

Whether you’re working on potable water lines, compressed air systems, or more corrosive chemical setups, the fitting material you choose can affect performance, longevity, and even safety.

Plastic Fittings: More Than Meets the Eye

Let’s start with the John Guest line—where most people begin (and for good reason). These fittings are well-known for their ease of use, quick installation, and excellent performance in low- to medium-pressure applications.

Acetal (POM) is the workhorse of the John Guest lineup. It’s strong, lightweight, and ideal for use with drinking water systems, ice machines, beverage equipment, and general plumbing. Acetal is NSF-certified, UV-resistant, and works well in most indoor environments.

For more aggressive media or chemically demanding environments, polypropylene fittings are a better match. They offer superior chemical resistance, especially with acids and alkalis, making them great for laboratory setups or certain chemical dosing systems.

Then there's nylon, which is newer to the scene but incredibly useful. Nylon push fittings offer higher temperature and pressure ratings than standard acetal, and they’re well-suited for industrial applications where plastic is preferred over metal due to cost, weight, or corrosion resistance.

So yes—plastic fittings are far from “one size fits all.” With John Guest’s diverse range, you can match the material to the specific conditions of your system and still benefit from the speed and simplicity of push-to-connect technology.

When to Step Up to Brass

While plastic is great for many setups, there are times when metal is a must. Brass fittings are a staple in the world of fluid control. They’re sturdy, have good corrosion resistance (especially in potable water), and can handle higher pressures and temperatures than most plastics.

You’ll find brass fittings in air compressor lines, plumbing systems, gas hookups, and fuel transfer applications. They’re also reusable and easy to work with. Just be aware that in high-chloride or acidic environments, brass may be prone to dezincification—so it’s always smart to check compatibility.

Stainless Steel for the Toughest Environments

If you’re working in harsh, high-pressure, or high-temperature conditions, stainless steel is the gold standard. It’s ideal for marine environments, chemical processing, food and beverage production, and pharmaceutical applications.

Stainless steel is incredibly durable, corrosion-resistant (especially 316 grade), and can handle just about anything you throw at it. It’s more expensive than other materials, but for mission-critical systems, it’s often the best investment.

Final Thoughts on Fitting Materials

There’s no single “best” fitting material—it all depends on the application. John Guest plastic fittings (in acetal, polypropylene, and nylon) are incredibly versatile and efficient for most low- to medium-duty systems. But when pressure, temperature, or corrosive media come into play, brass or stainless steel may be the better choice.

Need help deciding what’s right for your project? We’re here to help you make sure you’re using the right material for the job. Please reach out to our team to talk through your application and how we can help find the best fit for you.