Method of making a fluid tight connection between a tube and a connector, the method comprising the steps of: a) providing a flexible metallic tube having a circumferential surface and wall thickness (s), wherein the circumferential surface is helically corrugated, and wherein the tube has an end portion, b) providing a connector which comprises a retaining ring and a screw-in connecting piece, wherein the union ring has a first helical contour corresponding to the outer surface of the tube and can be screwed onto the end region of the tube on the outer surface by hand, and wherein the screw-in connecting piece has a second helical contour corresponding to the outer surface of the tube and can be screwed manually into the end region of the tube on the inside, c) screwing the retaining ring onto the end region of the tube, wherein for a free screw connection between the retaining ring and the outer surface of the pipe a clearance is provided, d) screwing the screw-in connecting piece into the end region of the tube, wherein, in order to achieve a free screw connection between the screw-in connecting piece and the circumferential surface of the tube, a clearance is provided, and wherein at least a section of the end region of the tube is arranged between the first contour of the retaining ring and the second contour of the screw-in connecting piece, e) pressing the retaining ring and the screw-in connecting piece against each other to at least partially eliminate the clearance, so that the portion of the end region of the tube is pressed in a fluid-tight and form-fitting manner against the first contour of the ring and on the second contour of the screw-in connecting piece, characterized in that in a further step f) the screw-in connecting piece is welded to the retaining ring and/or in a further step g) the retaining ring is soldered to the tube at one end of the retaining ring. a) providing a flexible metallic tube having a circumferential surface and wall thickness (s), wherein the circumferential surface is helically corrugated, and wherein the tube has an end portion, b) providing a connector which comprises a retaining ring and a screw-in connecting piece, wherein the union ring has a first helical contour corresponding to the outer surface of the tube and can be screwed onto the end region of the tube on the outer surface by hand, and wherein the screw-in connecting piece has a second helical contour corresponding to the outer surface of the tube and can be screwed manually into the end region of the tube on the inside, c) screwing the retaining ring onto the end region of the tube, wherein for a free screw connection between the retaining ring and the outer surface of the pipe a clearance is provided, d) screwing the screw-in connecting piece into the end region of the tube, wherein, in order to achieve a free screw connection between the screw-in connecting piece and the circumferential surface of the tube, a clearance is provided, and wherein at least a section of the end region of the tube is arranged between the first contour of the retaining ring and the second contour of the screw-in connecting piece, e) pressing the retaining ring and the screw-in connecting piece against each other to at least partially eliminate the clearance, so that the portion of the end region of the tube is pressed in a fluid-tight and form-fitting manner against the first contour of the ring and on the second contour of the screw-in connecting piece, characterized in that in a further step f) the screw-in connecting piece is welded to the retaining ring and/or in a further step g) the retaining ring is soldered to the tube at one end of the retaining ring. characterized in that in a further step f) the screw-in connecting piece is welded to the retaining ring and/or in a further step g) the retaining ring is soldered to the tube at one end of the retaining ring.