Abstract: A process for making tubes, channels and other relatively thin-walled elongated shapes having a unique degree of dimensional accuracy and stability in which the part after being shaped and only approximately sized is mounted on a mandrel having a larger coefficient of thermal expansion than the part. The mandrel and the part are connected at their opposite ends so that expansion of the mandrel first causes elongation and concomitant lateral shrinkage of the part and then lateral expansion of the part so that it is triaxially hot worked to bring it to its final hot size from which the part contracts to its finished size at room temperature. For maximum freedom from residual stresses and dimensional stability thermal sizing is carried out by heating to a temperature at least just above the recrystallization temperature of the part.