Abstract: An improved releasable coupling for a tube is disclosed. The coupling contains a socket with at least four stepped bores. Located within the first bore is a compresion means (such as a collar) which has an inner surface inclined to the axis of first bore. A collet is mounted within the compression means and is so configured that, when the collet is caused to move inwardly, the inclined surface of the compression means causes the jaws of the collet to move inwardly. The coupling also contains a tube support located within the second bore. At least four sealing means are disposed within the third bore: a first O-ring is contiguous with a first washer, which in turn is contiguous with a second O-ring, which in turn is contiguous with a second washer.