The top or stationary part of the C clamp is welded to the back side of the square tubing. Then the curved material is welded to the front side of the tubing. Then on the pivoting part of the C clamp I welded another piece of the curved material. For the curved material I used pieces of a railing. The inside curves were perfectly shaped for seat tubes. Since the end of the C clamp pivots, I used the two small diameter rods as slides to hold it straight. Hope this helps. If not I can take some close up pics. DG