Tube nuts are used in all types of automotive hydraulic lines, including brake fuel, oil, and transmission. To make a connection, place nut over the tubing with the threaded end pointed towards the end to be flared (repeat on the other end of tube). The tubes flare will be clamped between the nut and the flare seat when tightened. AGS Fittings include 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 clamshells, 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.