See if you can find a chart of drill and tap sizes. I usually try to use sizes that are most common so I can find nuts and bolts of those sizes.
Soemtimes I just round it the best I can, leaving the area to be threaded slightly large and work the die down on it. If it cuts without too much force, it will be fine, but dont force it too much or you'll break something. Make sure the tang is soft before you try to thread it. Lin
Edited: I was typing while Karl was. Karl is telling you right. Sometime the "shadetree" in me comes out.