Copper Capillary 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