Abstract: An improved coupling assembly (52) for rigidly securing the shaft (18) of a vertical pump (10) to the co-linearly spaced shaft (24) of a pump driver (22). A novel design provides a reduced uniform maximum diameter and obviates shaft threading and registration fits. The resulting assembly is, therefore, easier and less costly to fabricate accurately wherein pump shaft runout at the stuffing box face is no greater than 0.002 inches T.I.R. The coupling assembly of the present invention comprises a pair of cylindrical rigid hubs (54, 56) which may be secured to the pump and driver shafts (18, 24), respectively, by means of split rings (76, 78, 80, 82) for vertical thrust bearing; and an optional split spacer (64, 66) positioned between the hubs. Split shims (58) are employed above the pump-shaft rigid hub (54) to provide vertical position adjustment of the pump shaft (18) relative to the driver shaft (24).