Short definition
A flare fitting is a mechanical copper joint where the pipe end is flared outward — using a flaring tool — to a 45° (SAE) or 37° (JIC) cone that seats against a matching tapered fitting and is held by a threaded nut. No torch, no solder, no solvent. Most common in residential plumbing at gas-appliance connections and refrigeration lines.
What it is
The pipe end gets flared with a flaring block: clamp the tube, drive a cone into the end, and the metal forms a smooth bell-shaped flare. That flared end seats against the tapered cone of the flare fitting, and a threaded nut compresses everything into a metal-to-metal seal.
In US residential plumbing, 45° SAE flare is the dominant standard — used on gas appliance hookups, HVAC, and refrigeration. 37° JIC flare is industrial/hydraulic; not interchangeable with SAE.
Why it matters to a homeowner
You probably won’t flare your own copper. Modern flexible gas connectors (the coated stainless steel lines that connect a range, dryer, or water heater to the rigid black iron pipe) have integrated flare ends, so the homeowner-touched end of the connection is captive. The flare itself is on the connector, factory-made.
Where you’ll encounter the term: a refrigeration tech replacing an icemaker line, an inspector noting a non-flare fitting on a gas line where flare is required, or a quote specifying flare connections at appliance valves.
Common variants and what a flare is not
- Flare vs. compression. Flare requires modifying the pipe end with a flaring tool. Compression uses an unmodified pipe with a separate ferrule. Both are mechanical, no-torch.
- 45° SAE vs. 37° JIC. 45° is residential gas, refrigeration, HVAC. 37° is industrial. Not interchangeable.
- Single flare vs. double flare. Double flares are folded over for higher-pressure use (brake lines); single flares are standard for residential plumbing.
Common failure modes
- Cracked flare from over-tightening or off-center flaring.
- Under-flared joint — the flare is too small for the fitting cone, doesn’t seal even when tight.
- Reused flare with debris — slow leak.
- Wrong angle — 37° flare on a 45° fitting leaks immediately.