an apparatus for preventing the rotation of a nut with respect to a threa shaft , one version suitable for use on a plain threaded shaft and another version suitable for use on a threaded shaft having an axial keyway of rectangular cross section . the apparatus consists of a slotted and grooved nut and a tanged snap ring . the nut has radial slots across a face , and a circumferential groove which intersects the bottom of the slots . the snap ring fits over the nut within the circumferential groove , the tang extending down through the nut and engaging with the threaded shaft .