Sometimes it pays to pour yourself a cup of coffee and think things through a bit.
In this case, ask yourself how could a threaded race could end up there if it were (note the use of subjunctive mood) keyed in to the fork so it couldn't turn.
The answer is that it couldn't. So either the race isn't threaded and simply slides on, or the keyed part is separate from the threaded part.
Now, you can go back and read Andy's post for the solution.