Jerry found these bits and pieces in various scrap boxes. The pieces he used are marked in the photo. (A) A large piece of threaded rod and some nuts; (B) a piece of 2-inch gun barrel, which probably came from an anti-aircraft gun. It had been lying in the scrap box for years. (Any piece of heavy tube could be used.); (C) a big nut that became the spacer shown in the drawing opposite page; (D) a 1-1/2-centimeter-thick dropout salvaged from a profile cutter. It became Ring A also seen in the sketch.