There are many different ways of securing the propeller nut, including castelated nuts with split pin and cone nut with lock bolt, either having to drill through the shaft for a split pin or extra drilling and tapping the shaft end for the lock bolt.
Using a tab washer is a simple operation for use with a standard hexagon nut or cone nut with 2 flat sides, so as to lock the nut to the propeller.
The inner tab (between the 2 slits) on the washer is bent 90 degrees to the face.
After the propeller is fitted on the shaft taper, the tab washer is placed onto the shaft thread with the tab located into the propeller keyway. The nut is then tightened against the tab washer and the outer edges of the washer bent over the flats on the nut.