A header for a heat exchanger includes a first and a second cylindrical portion. The first cylindrical portion has a first diameter, and extends over a first length portion of the header. The second cylindrical portion has a second diameter that is smaller than the first diameter, and extends over a second length portion of the header. Tube receiving slots are arranged along the first length portion. An end cap is received into an open end of the first cylindrical portion, and is joined thereto to seal a first end of the header. An open end of the second cylindrical portion is arranged at a second end of the header opposite the first end to allow for fluid flow into or out of the header. A circumferential bead is located between the first and second cylindrical portions, and extends radially outward of the first cylindrical portion.