Abstract: A method of joining first and second flat sheet metal portions in overlapping relation one above the other to form a joint in the two sheet metal portions. Metal adjacent and spaced from one free edge of a first sheet metal portion is cut parallel to the free edge and expanded to form a generally U-shaped female receptacle arcuately domed and tapered inwardly and downwardly in a direction away from the free edge. The second sheet metal portion is cut in a truncated V-shape and the V-shape cut is bent to form a generally truncated, V-shaped male prong bent at an angle with respect to the second sheet metal portion. The first and second sheet metal portions are forced into overlapping engagement, one above the other, progressively, while directing the male prong into the female receptacle.