RE: GAS/GLOW HOW TO....
I get used tapered plugs from work for free (out of chevy 350's generally), cut off the hex part on the lathe which lets the ceramic part fall out easy, I leave some of the flat part behind the hex so I can grab it when I flip it around, next I cut off all but about 3 threads with the lathe and now tap to the 10mm threads (they are just the right size to tap without drilling, then flip it around again and clamp onto the threads with the chuck (it doesn't take much, and I do it with the intent of leaving it in the engine so it works fine) and trim off the other side right up to the taper, this makes the most compact 14mm to 10mm plug adapter you can get. If I'm going for a glow plug adapter I follow the same steps shy of tapping with the addition of making a plug to go in from the combustion chamber side out of aluminum that's a press fit, tapped to 1/4-32, before pressing in I put a dab of green loctite (sleeve retainer).