What Is a Flaring Tool? | Tube Sealing Basics

For the full breakdown, see our best Tubing Flaring Tool guide.

If you’ve ever tackled plumbing, refrigeration, or automotive brake work, you’ve met the problem a flaring tool solves: a plain cut tube can’t seal against a fitting, no matter how hard you tighten it. Flaring widens the tube’s end into a precise cone that seats against the fitting’s matching surface, creating a mechanical joint that holds up under pressure without solder or glue. The Copper Development Association notes that flare joints should match the tube’s outside diameter and flare angle, with 45° being the most common standard in U.S. work.

How a Flaring Tool Works

Flaring tools form a funnel-shaped lip on the tube end using a clamp block and a tapered cone. You hold the tube in the correct-size hole, then drive the cone down into the tube end until the metal spreads outward into the flare shape. Some tools are designed specifically for single flares, others for the stronger double flares used in brake and fuel lines, and some support a ratcheting action for more consistent results.

RIDGID’s catalog lists both manual flare tools and hammer-type models, while their precision ratcheting flare tools handle steel, stainless steel, hard copper, and brass tubing through a wall thickness of 0.035 inches (0.9 mm). That material range matters — not every tool can flare every metal.

How To Use a Flaring Tool: The Step Order

Getting a flare that actually seals comes down to preparation. Skip any of these steps and you’ll be re-cutting the tube.

1. Cut the tube squarely. Use a proper tubing cutter, not a hacksaw. A square end is the foundation of a correct flare.
2. Deburr the inside edge and chamfer the outside edge. Burrs left behind will tear the metal as the cone forms.
3. Insert the tube into the correct-size hole in the clamping bar, with the tube protruding to the height your tool specifies.
4. Tighten the clamp securely, starting with the nut closest to the tube so it grips evenly.
5. Place the yoke and cone over the tube end and drive the cone down until the flare forms. For double flares, the process includes an initial belling step, then folding the tubing back on itself to form a 45° double flare.
6. Keep the cone clean and lightly lubricated where the tool’s instructions call for it.

When the flare is done right, the cone should be smooth and even, with no cracks or thin spots. For choosing the right tool for your projects, our roundup of the best tubing flaring tools compares the leading models on material support and flare quality.

Common Mistakes and Material Limits

Most failed flares trace back to a handful of errors: an uneven or non-square cut, skipped deburring, or an improperly tightened clamp that lets the tube slip or deform. All of them are avoidable with patience on the prep steps.

Material compatibility is another trap. A flaring tool built for soft copper may struggle with stainless steel, and exceeding a tool’s wall-thickness limit — like RIDGID’s specified 0.035-inch ceiling — can crush the tube instead of flaring it. Always confirm that your tool supports both the metal and the tube’s wall thickness before you clamp down. Wear approved eye or face protection during any flaring work; the metal can spring unexpectedly.