Pipe fittings may also be used to form a hermetic seal at pipe ends and for other auxiliary functions. Fittings are manufactured in various shapes, depending on the intended purpose.Right-angle elbow fittings provide for a 90° change of direction, tees provide for branching in one direction, and double tees,or crosses, make it possible to branch in two directions. Sleeve couplings connect pipes in a straight section, and plugs and cap fittings are used to form a hermetic seal at pipe ends. Other fittings are used to connect the ends of pipes of the same diameter or different diameters. Fittings are manufactured from malleable pig iron, steel, and other materials.