Sweat Fittings

Ever hear the term capillary fitting and wonder if it had something to do with blood vessels? Don’t worry—it’s strictly plumbing. But it does involve a tight connection. Let’s talk about copper capillary fittings and why they’ve stood the test of time.

 
What Are Copper Capillary Fittings?
Copper capillary fittings are soldered pipe connectors that rely on a process called capillary action. That’s when molten solder flows into the narrow gap between the fitting and the pipe by surface tension.

Here’s how it works:

Heat the joint
Apply solder to the edge
The solder is drawn into the joint, creating a sealed connection
It’s a strong, watertight bond—no screws, clamps, or compression needed.

What Makes a Fitting “Capillary”?
The design is what makes these fittings so effective:

The fitting has an internal socket slightly larger than the pipe
When heated, this tight gap allows solder to flow in naturally
The result is a clean, compact, and permanent joint
Capillary fittings are also called

Today, let’s dive into a topic that’s super important but often overlooked - threads. And no, I’m not talking about the latest social media buzz; I mean the kind that keeps your pipes nice and leak-free.

So, here’s a question I hear all the time: Are copper fittings NPT, or National Pipe Thread?

Quick answer? Some are, but honestly, most aren’t.

Let’s unpack this, thread by thread.

What Is NPT Anyway?
NPT stands for National Pipe Tapered Thread. It’s basically a standard we use here in the U.S. for threaded fittings in plumbing, gas lines, and air systems.

These threads are tapered, which means they get tighter as you screw them together. They’re designed to create a mechanical seal, often using good ol’ pipe tape or some thread sealant. You’ll typically find them in steel, brass, and plastic fittings.

Just a few keywords to keep in mind: NPT fitting, NPT pipe, NPT threads, check valve, globe valve, plug valve.

But here’s the kicker...

Most Copper Fittings Are Not NPT
Copper fittings? Well,