A coupling is provided that includes a shaft, a hub, a retainer and a fastener. The shaft includes a plurality of shaft splines. The shaft splines are arranged circumferentially about an exterior of the shaft. The hub includes a plurality of hub splines, a hub bore and a hub fastener aperture. The hub splines are arranged circumferentially about the hub bore. The hub splines are mated with the shaft splines. The shaft is within the hub bore. The retainer includes a plurality of retainer splines, a retainer bore and a retainer fastener aperture. The retainer splines are arranged circumferentially about the retainer bore. A first of the retainer splines circumferentially overlaps and is axially next to a first of the shaft splines. The shaft is within the retainer bore. The fastener is within the hub fastener aperture and the retainer fastener aperture. The fastener connects the retainer to the hub.