Improved impeller attachment method

A pump is provided having an impeller in combination with a power transmission shaft. The impeller has a tapered bore with impeller threads. The power transmission shaft has a shaft end with tapered threads configured to couple directly to the impeller threads of the tapered bore of the impeller, to transmit torque directly through the tapered threads, and to provide self axial or radial alignment even if the coupling of the tapered threads and the impeller threads of the tapered bore start out of alignment. The tapered thread configuration substantially reduces investment in lifting equipment and time by maintenance personnel because it eliminates the need for maintenance personnel to precisely align the impeller threads and the tapered threads before attaching or removing the impeller and the tapered threads release much more quickly from the impeller than a standard thread configuration, reducing the number of turns the power transmission shaft must be rotated by hand to free it from the impeller.