The ideal way is a threading machine. Barring that, a hobby lathe. Barring that, a portable threader. Barring that a ratchet threader.
Ratchet threader might be easiest and most cost effective. And will keep you from getting tired. You also might consider getting a high quality die. Possibly carbide. Also, use a threading fluid. It will make it easier and the dies will last longer.
Looks like this:
