You cannot connect a straight metal pipe to a brake caliper; it will leak under pressure. A flaring tool creates a flared end that seals against the fitting. The metal tube is clamped into the tool's bar. A steel adapter and a threaded cone press are then used to fold the tube end. For brake lines, you must make a double flare or an ISO bubble flare. This double-folds the metal to prevent the pipe from cracking under high hydraulic pressure.
Mechanic Glossary
Flaring Tool
A clamping bar and cone press tool set used to form a single or double flare on the ends of metal brake, fuel, or transmission lines.
Frequently Asked Questions
A single flare simply spreads the tube end outward. A double flare folds the tube edge back inside itself first, making the wall twice as thick to resist high brake pressure.
Yes. Most flaring tools are designed for copper, brass, aluminum, and mild steel lines. Hardened stainless steel lines require heavy-duty hydraulic flaring tools.
The tube was likely cut unevenly, or you did not file down the internal burr before flaring. Always deburr the tube inside and out first.