Abstract: A stabilizer sleeve, or other sleeve, to be releasably mounted on a drill collar for centering a drill string in a well bore, includes an outer stabilizer sleeve to be mounted on the cylindrical periphery of the drill collar and having an internally threaded bore, the threads of which have conical roots, receiving an externally threaded yieldable sleeve member placed over the drill collar, the crests of the external threads also being conical, rotation of the yieldable member threading it into the stabilizer sleeve and effecting its contraction until its internal surface contacts the periphery of the drill collar, further rotation and tightening of the sleeve member in the stabilizer sleeve compressing the sleeve member against the drill collar periphery, with the crests bearing against the root portions of the internal sleeve threads to secure the sleeve frictionally in position on the drill collar.