Abstract: An obround header of obround cross-section for a heat exchanger and a process for forming such a header. An obround header of obround cross-section has sidewalls with flat inner and outer portions. A curved transition between the opposing sidewalls minimizes stress concentrations within the header. The flat portions of the sidewalls provide a planar surface, for which it is easier to drill tube openings and access plug holes and install tubes and plugs. The flat surfaces, along with the opposed holes and openings, make installing and cleaning the tubes easier. A fluid nozzle provides an inlet or outlet for the fluid. The process for making the flat sidewalls is by forming material from a round cross-sectional geometry to an obround shape.