Flared connectors should not be confused with compression connectors, which are generally not interchangeable. Lacking a compression ring, they use a tapered conical shaped connection instead. A specialized flaring tool is used to enlarge tubing into a 45º tapered bell shape matching the projecting shape of the flare fitting. The flare nut, which had previously been installed over the tubing, is then tightened over the fitting to force the tapered surfaces tightly together. Flare connectors are typically brass or plastic, but stainless steel or other materials may be used.
Although flare connections are labor-intensive, they are durable and reliable. Considered more secure against leaks and sudden failure, they are used in hydraulic brake systems and in other high-pressure, high-reliability applications.