For damage that light, a die is way over kill and you may do more damage than good. Even when you get the die, you will likely have to file the damage out before starting the die.......my advise DON"T use the die. Just clamp the valve in a vise and use a small triangular file, about 1/4 on a side or less, to open up the threads. You can find these at most any hardware store. A set of needle files (very small files) would also be fine. It's very easy, just lay the file in the thread just ahead of the damage and gently push it into the damage letting the file follow the existing thread. If you have never done it, get a cheap (larger) bolt, ding the threads and practice on it. The brass will be way easier to cut. Yes you will lose a little chrome but it's not a problem.