In the drawing, FIG. 1 is a longitudinal section through a fitting on a flared pipe end prior to tightening, FIG. 2 is a fragmentary section after tightening the FIG. 1 fitting, FIG. 3 is a longitudinal section through the tool for forming the flare, FIG. 4 is a section on line 4--4 of FIG. 3 and FIGS. 5-9 inclusive are fragmentary sections showing successive stages in the forming of the flare.