Abstract: A locking nut assembly in which a dished washer (16) has a cylindrical bore (19) which is a close runner fit on the external cylindrical face (15) of a spigot (12) formed under the head (11) of the nut (10). In use the washer (16) is flattened, the bore (19) contracts and grips the spigot (12) which is thereby deformed inwardly so that the thread (14) within the spigot is forced into close contact with the complementary thread on a bolt with which the nut is used.