Compression unions are used in low-pressure applications such as: air, oil, and water. They are generally used to connect lengths of copper, brass, and aluminum tubing. To make connection, place the nut and then the sleeve over the tubing and then insert tube into the fitting body. When tight, the wedging action of sleeve between body and nut create a leak free connection. Compression Unions come in a retail-oriented clamshell package in a quantity of 1, a bulk Ziploc bag in a quantity of 10, or a small plastic bag in a quantity of 1.