PURPOSE: To preclude infiltration of brazing material into screw holes, by a method wherein annular grooves are formed on respective joints of an inlet port and an outlet port around respective annular projections of respective joints, while annular projections are formed on these joints around the annular groove between said annular groove and screw holes.

CONSTITUTION: Molten brazing material for brazing a joint 1 to a core 13 creeps up by the surface tension and capillarity thereof through a gap between the annular projection 9a of an inlet joint 1 and the holes of a core plate 2 to be engaged with the projection 9a, while the brazing material on the surface of the core plate 2 tends to flow along the lower surface of the joint into screw holes 7 for attaching a pipeline. However, the annular groove 1a and the annular projection 1b hinders the flow of the brazing material so that the brazing material will never invade into the screw holes 7.