Originally Posted by juld0zer

the spring washer is the big washer that goes beneath the big axle nut. you need two per side because the Kawasaki nut is *shorter* than the OEM axle nut.

the Kawasaki nut is actually physically almost identical in size but since it is the castellated type (nut with inbuilt castle-like top), the castellated slots fall short of the cotter pin hole in the axle.
For this to be an effective fix, the slots must have a cotter pin driven thru them, hence the need for an extra washer.