Abstract: A manifold assembly for use with heat exchangers comprises a unitary tank having a semicircular cross-section and a unitary header plate which also has a semi-circular cross-section, the outer diameter of the tank being substantially equal to the inner diameter of the header plate to allow the tank to be inserted into the header plate. A plurality of transverse tube holes are formed through the header plate along its longitudinal center line for receiving the tubes of the condenser or evaporator. A flange or lip is formed around the tube holes to provide both a tube lead-in and a joint filleting pocket. A plurality of opposed transverse slots are formed through the tank and header plate along their longitudinal center lines to receive baffles therein for locking the tank and header plate together during assembly and for adjusting the flow pattern during use. The baffles are configured to engage the inner walls and sides of the slots.