Lock washer with tab for all 10 mm threads
The tab grips in the surface and the washer is bend up. So the nut is secured.
Recommended to use for the 10 mm nut on all alternators (6 and 12V)
Hint: At some Dnepr gears the bore of the sprocket is missing. If you drill a 3 mm deep hole, you do not need the split pin.