You need a thread-cutting die for the proper thread spec. Most forks will be English thread (1" x 24tpi) but there are exceptions. Italian thread is close enough to English that you can use the same die. French thread (25mm x 1mm) requires its own die. And there are odd-ball Raleign 1" x 26tpi and oversize 1-1/8 x 26tpi and 1-1/4" x 26tpi forks as well. These tools tend to be too expensive for one-off projects, and work best in experienced hands. Check your local bike shops to get the work done.