Abstract: A sensor probe is affixed at an end of a probe adapter which includes an extended portion which is radially flexible but torsionally stiff. A guideway which passes from an accessible location in a machine to the vicinity or the target surface guides the sensor probe to its operative location. Final positioning of the sensor probe is attained by abutment of a forward shoulder on the probe adapter with an abutment shoulder fixed to the machine a predetermined distance from the target surface to be monitored. This permits removal and replacement of sensor probes without requiring final adjustment of the replacement sensor probe. One embodiment of the invention permits final adjustment and locking of the sensor probe in position after full assembly of the bearing housing by providing a star wheel on an adjustment sleeve which, after adjustment is locked in position by a setscrew.