The jig has a rigid frame (1) positioned on a horizontal pipe (5) and clamped in place with a screw (2). A further pipe section is placed next to the first and a curved frame (3) is attached to it. a lever (7) is pressed to lower both chains (6) which are suspended in the frame at the left and right of the pipe to be clamped and the second pipe is pressed into the first. A holding frame (12) at each side of the main frame supports rollers to the left and right of the pipe for parallel movement of the second pipe section with respect to the first.
