Originally Posted by FBinNY

Use a triangular file as explained above. The problem with chasing is that the chaser will also want to pick up the bad thread and you'll be further establishing the cross thread.

I generally don't bother trying to save the first threads on hubs, There's plenty of thread engagement, so I use a flat file to create a bevel at removing the first thread or so. This not only solves the immediate problem, but reduces the chance of cross threading later on.

BTW- a half mill file is best for this kind of work because it leaves a better finish.