Quite often, the top of that thread gets bulged when someone tries to remove the steering wheel by hammering on the top of the thread instead of using a puller. The spline has a gradual taper, which locks the steering wheel tight onto the shaft and requires a jackscrew puller to break the bond. When someone tries to remove the nut, it gets stripped, and the top few threads also get damaged. If there are a few undamaged threads near the bottom,, sometimes some careful filing or grinding to taper the top few threads will allow a die to get started and straighten up what's left. Be careful- - - -you'll only get one try at this procedure! If it works, a new nut solves the problem. Just don't get too energetic when tightening it!
Jerry
