Abstract: An apparatus for coupling concentric cylindrical members through the selective radial enlargement of one of the coupling components comprising a fixed collar having a cylindrical interior bore of a common diameter and with an exterior cross section of varying diameters. The apparatus further includes an adjustable component which has an upper half and a lower half and a central bore extending therethrough with an inboard end forming a flange of an intermediate diameter positionable over the intermediate section of the collar and having a enlarged diameter thereadjacent for being positioned over the outboard section of the collar and having an outboardly tapering intermediate section with its greatest diameter at the outboard end and its smallest diameter at its inboard end joining at its inboard end with the enlarged diameter.