I inherited a Supermetric geometric die with my lathe, but only recently figured out how to set it up. After watching a few useful videos on YouTube, I settled on a setup that seems to work. The key point is that the die is mounted in the tailstock, which is free to slide along the ways.
After the threads were cut -- which was easy once the right diameter was turned -- I filed a head. The slot was a little off center, but not to bad for a first try. Edwin also tried to make a screw and didn't do too badly.