Abstract: A spinner tool comprises an elongate, cylindrical housing including a portion having elongate, axially extending, angularly disposed slots formed therethrough at circumferentially spaced points. An impeller is mounted within the housing and comprises circumferentially spaced, axially extending blades which are each J-shaped in cross-section so that the impeller is rotated in response to radially directed fluid flow entering the slots of the housing, but is not rotated in response to axial fluid flow. The impeller is mounted on a shaft which is supported by bearing structure that is substantially self-cleaning under the action of fluids flowing through the housing. A plurality of magnets are secured to the shaft for rotation under the action of the impeller, and a reed switch is positioned for actuation by the moving magnets to generate an output signal indicative of rotation of the impeller. Electronic circuitry is provided in the housing for amplifying and shaping the output signal from the reed switch.