Abstract: A connecting arrangement comprising a threaded sleeve of synthetic plastic material and a tube portion having a pipe thread. The threaded sleeve contains an insert nut with an internal thread and a synthetic plastic ring which is engaged by the pipe thread of the tube portion. The tube portion has at its forward end a supplemental sealing ring which sealingly engages a sealing region of the synthetic plastic ring. The sealing region is spaced from the axial ends of the threaded sleeve and has an inner diameter which is smaller than the outer diameter of the sealing ring. A further seal may be provided by disposing an adhesive sealing mass in an annular groove on the tube portion such that the mass adheres the tube portion to the sleeve when they are connected.