A tube header for a heat exchanger includes a header plate having two major dimensions defining a header plane. The header plate has a row of oblong passages extending through the header plate. Each passage is bordered by a ferrule monolithically formed with the header plate. The ferrule has a surrounding wall extending perpendicular to the header plane. A transitional area between the ferrule and the header plate has a reduced thickness that is smaller than the wall thickness of the ferrule. This transitional area provides a flexible hinge-like function for compensating dimensional changes during thermal cycles of a heat exchanger.