Ags fittings are comprised of tube nuts, Unions (couplers), and adapters; used primarily in the automotive hydraulic braking, fuel, and transmission systems. Fittings are offered in a variety of Packaging options, including: retail clam-shells, bulk boxed, and plastic tray assortments. automotive hydraulic brake fittings are formed to work with either SAE inverted double flare (domestic and Japanese vehicles) or ISO Bubble flare (European and British vehicles). in either case, the fitting (whether a tube nut, union, or adapter) must be selected to match the end form of the tube or port it will be mating to or a proper seal will not be possible. Use for 5/16" domestic fuel and transmission lines.