Unions are used to join two brake, fuel, or transmission lines together. This may be needed, for example, in long runs from the dual master cylinder to the rear axle. Match the thread and flare type to the lines being connected. It is important that both flare type and thread match for a leak-proof connection. 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.