A flare fitting connects tubing through a formed, flared tube end pressed against a matching seat. A nut holds those mating surfaces together. The seal is made at the flare and seat, rather than simply at the nut's threads. Tube material, flare geometry and the identified fitting system determine compatibility.
A flare fitting connects tubing through a formed, flared tube end pressed against a matching seat. A nut holds those mating surfaces together. The seal is made at the flare and seat, rather than simply at the nut's threads. Tube material, flare geometry and the identified fitting system determine compatibility.
The sealing surface is the important part
The Copper Development Association's handbook describes flared joints for copper tubing, including the need for a suitable, smooth and correctly formed flare. Swagelok's end-connection guide distinguishes different flare and thread families used on its products.
These are product and connection descriptions, not approval to use every flare system on a home's water or gas piping. A flare angle, size designation or thread that appears to match can still belong to a different fitting family. The manufacturer and applicable installation requirements control the actual connection.
A compression fitting uses a ferrule rather than the same formed tube-end seat. A tapered pipe-thread fitting seals by another mechanism. The NPT thread entry explains that separate connection label. Identifying those differences comes before choosing replacement parts or sealing materials.
Why appearance is not enough
An uneven or damaged flare may not contact the seat correctly. Tubing condition, alignment and support also affect whether the assembled connection can remain sound. Tightening a nut harder does not establish that a damaged sealing surface has been repaired.
A connection that was suitable for one tube material or operating condition is not automatically suitable for another. Verify the allowed fluid, pressure and temperature with the actual component instructions. A thread size alone supplies only part of that information.
Where gas is involved, this terminology does not authorize a homeowner to disconnect or remake the joint. If gas is smelled, leave the area and obtain emergency help from a safe place.
What to identify in a quote
Ask for the exact fitting family, tubing material, size and end-connection description. A repair scope should explain whether the existing sealing surfaces can be used under the manufacturer's requirements or need replacement.
Our compression ferrule entry explains the other common tubing connection. See thread sealant selection for why a nut that provides clamping force is different from threads that themselves need an approved sealing method.