Set the gears on the standard change gear lathe to the size threads you want on the screw. Adjust each setting until they are set to standard guidelines. For a 1/4 inch screw with 24 threads per inch, set the decimal equivalent on the drill to .2090. For example, a 5/16 inch screw with 20 threads per inch, set the decimal equivalent on the drill to .2656.
Lock the metal bar into the lathe. Secure it tightly with the grip knob.
Turn on the lathe and gently move the cutter bit along the metal rod. The cutter bit will carve away the metal rod and create a thread on the metal rod.