"Andy Dingley" wrote in message

I am looking for a 1/2" or 3/4" threaded steel rod (or a bolt at least 4"
long) that has been cut so that it has two flat sides.

Only 4" long ? Rod, few nuts, vice and a file.

If he's going to file two edges flat and still have the threaded sides
workable with a nut, I'd be more inclined to use a die to clean up the
threads. Of course, it may depend on the amount of flatness needed and how
fine the files is.