Abstract: A replaceable stabilizer comprises a steel sleeve with fixed blades adapted to be installed over the reduced lower box end of tubular rotary drill steel member prior to insertion of the taper threaded pin of a drill bit into the taper threaded drill steel box. The drill steel member may be a special sub or a regular length of drill steel with modified lower end. An internal straight thread at the upper end of the sleeve screws onto an external straight thread on the drill steel box. An annular rubber gasket secured to the upper end of the sleeve is clamped between the upper end of the sleeve and a shoulder on the steel between the main body and the reduced box end thereof. An inturned flange at the lower end of the sleeve is clamped between a shoulder provided by the mouth of the drill steel box and a shoulder on the drill bit around its taper threaded pin. Make up of the pin and box forms a rotary shouldered connection.