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In this case, the tower is supposed to carry a downward force, and a lateral force, but not a longitudinal force.
These may have, for each conductor, an insulator string hanging down from the tower, or two strings making a "V" shape. In either case, sometimes several insulator strings are used in parallel to give higher mechanical strength. These are used where a transmission line continues in a straight line, or turns through a small angle. In other cases, a tension tower (C or D Towers) is used.