Abstract: A coupling includes at least one thin-walled sleeve which forms an axially extending defining wall of a substantially annular chamber. The chamber is arranged to be supplied with a pressure medium to elastically deform said sleeve in a radial direction into clamping engagement with a surface on an element which is to be connected to the coupling, the shape and dimension of said surface substantially corresponding to the shape and dimension of a surface on the sleeve remote from said chamber. The chamber has extending therefrom a channel arrangement which is arranged to cooperate with coupling-release means which can be activated by relative movement between said surfaces, or by a given torsional deformation thereof, to a state in which pressure medium can flow through said channel arrangement from said chamber to relieve the chamber of pressure acting therein.