This is a handy little tool we use here in the shop. It is essentially a holder which will hold either a 13/16" or 1" button die which rotates on the shank mounted in the lathe tail stock. One runs the die holder up to the work with the lathe spindle turning the part to be threaded (slowly), hold the holder until the desired length of thread has been generated and then release. Stop the lathe, reverse the spindle holding the holder until the die disengages from the part. In this manner one can generate threads that are geometrically correct rather than off at some angle to the axis of the part. There are 3 shank sizes available (and sold separately from the die holder).