A bubble flaring tool is used to create International Organization for Standardization (ISO)-compliant flares on the ends of tubing. A double flaring tool, on the other hand, is used to create Society of Automotive Engineers (SAE) double flares. The two types of flares are not interchangeable and require different tools.
There are several types of bubble flaring tools, but all work on the same principle. Essentially, they grip the outside of the tubing while a pressure screw is tightened against a mandrel to form a ridge, or bubble, at the end.
Double flaring requires a two-step process. The tubing is clamped while its end is formed, then folded back on itself to create a double flare.
Flared tubing seals internally, so should not be exposed to liquid sealants, or liquid of any kind, during installation. If the thread of tubing is wet, the quality of the joint will be suspect.
