Maybe you'll believe Sheldon Brown regarding French forks:

"French headsets use a different type of keyed washer than others. Instead of having a groove machined in the threads, the rear part of the threads is filed flat. French headsets commonly used a serrated keyed washer, with matching serrations on the threaded bearing race. This makes French headsets slightly harder to adjust, but once they are adjusted, they hold their adjustment better than conventional designs."