Abstract: A heat exchanger includes a pair of manifolds, each of which has a plurality of axially spaced oblong slots. A plurality of generally flat tubes extends between the manifolds and individually through the slots for providing fluid communication between the manifolds. A plurality of radiation fins extends between adjacent flat tubes. At least one of the manifolds comprises a single formed rectangular sheet member having a seam formed from connection portions on each side edge of the sheet member. Each of the side edge connection portions includes an interlocking formation of tabs and recesses, at least some of the tabs deformed as the side edge connection portions engage each other in the circumferential direction. The interlocking formation provides an interconnection which is easier to form and after brazing less subject to burst when under pressure. End caps are provided on each end of the manifold, which include a concave shape which assists in holding the end caps in place when the manifold is pressurized.