10 years ago I was looking at doing the same thing. Andrew Coholic from Canada was in need of a TD .09 glow head at the time and traded me for a tap he had made.
Below is his response to how he made it. Good luck, Greg
--- Andrew Coholic wrote:
---------------------------------
To make the tap, I cut the thread first, then mill the
grooves, and then lightly hone to remove any burrs, and then
finally case harden the cutting surface using Casenit compound.
Remember, cut only aluminum and non-ferrous metals, it is not
hard enough to cut steels.