Header plate for use in a heat exchanger

A header plate ( 20 ) is provided for receiving the flattened tubes ( 14 ) of a heat exchanger. The header plate ( 20 ) includes a plurality of tube receiving openings ( 26 ), with each of the openings being surrounded by a flange or collar ( 28 ) that extends from a base wall ( 24 ) of the header plate ( 20 ) towards the heat exchanger core ( 12 ) to surround the exterior cross section of the associated tube ( 14 ). Each of the flanges ( 28 ) is shaped to conform to the exterior of the associated tube ( 14 ), and a blend radius R is provided at the interface between the base wall ( 24 ) and the flange ( 28 ). The blend radius R has a size that increases from a radius R 1 central to the length of a long side wall ( 30 ) of the flange ( 28 ) to a radius R 2 central to the length of a shortside wall ( 32 ) of the flange ( 28 ).