A coupling includes a coupling housing and a coupling member. The coupling housing consists of a first housing part and a second housing part capable of being screwed together axially. Each of the first housing part and the second housing part has an internal conical surface, wherein, in a position that the first housing part and the second housing part are screwed together, the inner circumference of each of the internal conical surfaces generally lessen towards outward ends thereof, respectively. The coupling member is situated in the housing for clamping a tube inserted in the coupling housing. The coupling member is influenced axially by a conical clamping ring by cooperation with the conical surface in the first housing part and influences a resilient ring which causes sealing between the tube and the second housing part. One end of the coupling member is shaped as axial, flexible fingers separated by splits. As the first housing part and the second housing part are screwed together, the free ends of the fingers contact the resilient ring and are forced along the conical surface in the second housing part so as to force the resilient ring along the conical surface of the second housing part, whereby the resilient ring is compressed against the tube.