Square to Round The transition piece shown in figure 8-18 is used to connect round and square pipes. It can be seen from both the development and the pictorial drawings that the transition piece is made of four isosceles triangles, whose bases connect with the square duct, and four parts of an oblique cone having the circle as the base and the corners of the square pipe as the vertices. To make the development, a true-length diagram is drawn first. When the true length of line 1A is known, the four equal isosceles triangles can be developed After the triangle G-2-3 has been developed, the partial developments of the oblique cone are added until points D and K have been  located  Next  the  isosceles  triangles  D-1-2  and K-3-4 are added, then the partial cones, and, last, half of the isosceles triangle is placed at each side of the development. Rectangular  to  Round The  transition  piece  shown  in  figure  8-19  is constructed in the same manner as the one previously developed except that all the elements are of different lengths. To avoid confusion, four true-length diagrams are drawn and the true-length lines are clearly labeled. Connecting  Two  Circular  Pipes The following paragraphs discuss the developments used to connect two circular pipes with parallel and oblique  joints. PARALLEL  JOINTS.—The  development  of  the transition piece shown in figure 8-20 connecting two circular pipes is similar to the development of an oblique cone except that the cone is truncated The apex of the cone, 0, is located by drawing the two given pipe diameters in their proper position and extending the radial lines 1-1₁ and 7-7₁ to intersect at point 0. Fit the  development  is  made  to  represent  the  complete development of the cone, and then the top portion is removed. Radius settings for distances 0-2₁ and 0-3₁ on the development are taken from the true-length diagram. Figure 8-18.—Development of a transition piece—square to round. 8-14