Abstract: Stabilizer apparatus for a drill string or other running string, including a body structure forming part of a rotary drill string and a stabilizer positioned on an end portion of said body structure, the stabilizer comprising a stabilizer sleeve having a conical interior surface which is shrink-fitted onto a mating external conical surface of such body structure by fluid pressure actuated or hydraulic means, permitting a safe, strong interconnection between the stabilizer and the drill string body structure, which stabilizer can be readily removed when necessary and replaced with another stabilizer similarly shrink-fitted onto the drill string body structure.