Abstract: An improved device for adjusting the running clearance of a pump impeller is shown and described. In a preferred embodiment, an annular adjustment member is positioned adjacent to a pump impeller and the pump housing, the impeller being spaced from the adjustment member and housing by a predetermined distance. The adjustment member is selectively moved towards and away from the impeller, and lockable in any desired position. The adjustment member is moved in an axial direction by loosening a plurality of clamp nuts, and turning adjustment nuts until the annular adjustment member bottoms out on the impeller. The annular adjustment member is then backed off until an end surface of the adjustment member is spaced from the end surface of the impeller by the predetermined distance. The adjustment member is locked in the new location, thereby resetting the running clearance of the pump.