a mechanism for accurately positioning a well tool in axially concentric relationship to a well conduit comprises a housing having a plurality of stabilizer linkages mounted thereon with one end of each linkage being pivotally secured to the housing and the other end free to move in an axial direction . a compression spring engages a force transmitting connection to the other ends of the stabilizer linkages to bias same to a radially expanded position engaging the conduit wall . the connection between the compression spring and the stabilizer linkage includes two telescopically related sleeve elements which are secured together by a shear screw . in the event that the stabilizer linkage becomes stuck in the well , upward jarring movements of the housing will shear the shear screw and permit the stabilizer linkages to collapse radially inwardly and thus permit removal from the well .