Abstract: The device comprises a clamping jaw and a two-piece union nut. The clamping jaw is U-shaped in longitudinal section and straddles the end of the pipe so that it surrounds this pipe end from inside and from outside simultaneously. The two-piece union nut is composed of a first part and a second part which is inserted between the first part and the outer leg of the clamping jaw. The second part is provided with a left-hand external thread which meshes with a left-hand internal thread of the first part. Every location to be made tight within the device is sealed twice when the union nut is tightened, so that the connection is completely fluid-tight.