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The method of making a series of similarly shaped structural elements adapted to occupy spaced positions in a constructional assembly, comprising the steps of forming the individual elements of said series as a structural member having a plurality of angularly related faces similar to each other in shape but differing in size so that the outer contour of a smaller element is substantially congruent to the inner contour of a larger element, by corrugating a piece of sheet metal so as to include the angularly related faces of all said elements connected with each other along their congruent contours respectively, and each part of each element being spaced from the corresponding part of the adjacent element by a distance which is proportional to the spacing which such portions will have in the finished assembly, and separating the similarly shaped elements of said blank by cutting the blank along spaced parallel lines which are located in corresponding positions in adjacent portions.