Originally Posted by
FBinNY
Headsets without keyed washers (forks without keyways) are also hard to keep adjusted and tend to loosen very slowly over time. This is harder to fix if the fork doesn't have a keyway, and might call for locktite in the locknut threads.
I hand file the keyway into the forks I build. It doesn't have to extend all the way to the end of the threads; but just far enough to hold the toothed washer.