The brass flare nut works by compressing the flared end of a piece of tubing against the flare fitting and creating a seal that holds the two pieces of tubing together. This type of fitting is often used in refrigeration systems to connect refrigerant lines to other components of the system such as valves, regulators, and service ports.

There are several types of brass flare nuts available each designed for specific applications and uses. Some of the most common types of brass flare nuts include SAE flare nuts, 45° flare nuts, inverted flare nuts, 90° flare nuts, reducing flare nuts, and double flare nuts.