Abstract: A single flare tube, and a joint structure of the single flare tube makes a flare of the single flare tube hardly deformed plastically. Additionally, a tensile stress remains lower and is lower when the single flare tube is fastened. A joint structure of the single flare tube coupled with a union includes a single flare tube having a tube and a flare, a flare nut having a thread and a through-hole that receives the tube of the single flare tube, and a union having a thread for coupling with the thread of the flare nut. A width of a narrow inner circumferential groove of a radially outward extending part of the flare is substantially zero and stays substantially zero when the single flare tube is pushed against and coupled with the union by fastening the threads of the flare nut and the union together. Additionally, an internal diameter of the inner circumferential groove preferably is smaller than an external diameter of the tube.

Abstract: In a workpiece joining method using a joining jig, a distal end portion of a bolt shaft is inserted into each hole of at least one workpiece, and a sleeve is disposed onto a distal end portion of each bolt shaft. Then, an upper die of the joining jig is lowered toward the workpiece supported on a lower die so that while the workpiece is being pressed toward base end portions of the bolt shafts, a tightening portion of each nose provided on the upper die draws the outer wall of the corresponding sleeve, thus tightening the sleeves. As the tightening process progresses, the tightened portion of each sleeve progressively enters a relief portion formed immediately above the tightening portion. The thrust of the noses does not directly acts on the bolt shafts in the direction of their axes, so that the joining jig can apply a sufficient tightening force without being restricted by the strength of the bolt shafts.