Abstract: A self-locking propeller nut, suitable for marine drive trains which involve a great deal of vibration, is disclosed. The nut, which has a nose-cone shaped exterior similar to conventional propeller nuts, is molded integrally of semi-rigid plastic. At its center is a threaded bore wherein the thread diameter tapers narrower into the nut and wherein the thread spacing is slightly different from that of the propeller shaft end. The threaded bore lies in an inner cylindrical body which is recessed and connected to the housing in such a way as to further promote retention of the nut on the shaft.