Sometimes a need arises for threading a hole with non-standard machine threads. Buying one locally is rare and not an option. I will show you how I made one in a short time. http://www.techshop.wsMaterials and tools needed:
Lathe Threading Bit
Torch (to heat steel to red hot)
Drill Rod Stock or Hardenable metal
Turn metal stock to desired diameter on metal lathe.
Turn 6 degree taper to less than thread drill size. This will allow the tap to start more easily.
Thread Metal stock on lathe to desired thread pitch (i.e. ½ -28 for AR-15 Flash Suppressor).
Mill grooves in threads. Choose mill that will leave less than 50% threads after cutting 3 or 4 grooves. Cut 4 flats for Wrench or Tap Handle near end of threads. If making 4 grooves then cutting the flats is easier.
After cutting the first flat, turn the threads 90 degrees and use a square to ensure 90 dregrees.
Continue cutting the other grooves and flats.
Cut off tap from rod at end of flats with metal saw.
Return tap to lathe to center drill end with flats. Use small center drill.
Hold tap on flats with Vice Grips or pliers. Heat with hot torch till threaded end becomes orange red. Be careful not to melt threads. Then quench in water quickly. Tap will be hardened and brittle.