I need a tap to extend the threads in the head of a light and can't figure out what the thread is, it doesn't seem to match anything I can find in the various charts out there on the intertoobz.
Major is .840" (21.3mm), the pitch is an easy one at .050", or 1.5mm. Is this M22 x 1.5? Or the other possibility, it's not a standard thread at all, but something invented on-the-fly over in Chinese Flashlight Factory land. I sure hope not.
If the threads are really lose its probably 22mm. Otherwise its one of my threads. Just make it work.
Being it's aluminum could you go up to the next closest size up?re-drill and then re-tap ?
Close, the major for that m22x1.5 is “.866” iirc, more than likely it’s a wrong set up. It’s only .026 (0.66mm) out though, they probably did set up for that M22x1.5 thread and it went out of set after final setup, or they didn’t setup right for coolant shrinkage, you might get away with it if there’s enough to work with, with the tubes size though ?.
The head is .945"/24mm OD. Existing ID on the female thread in the head is .812".
It can't be drilled out bigger and rethreaded, it has to fit back on the original battery tube. I just need the head threaded deeper, with something approximately compatible with the original thread, so the pill can screw in farther.
I need threads only about 6mm deeper/closer to the bezel, so only about 4-5 full threads more than it has now. How much of a nightmare is it going to be to do this with a tap? Cause I'm sure the original threads were cut on a lathe, not with a tap. I know it will have to be clamped tighter than a tight thing, perhaps it will survive intact?
The thread can’t be removed from that section that is being screwed in? Hope that makes sense.
I think Mrs DNF means, instead of extending the thread, remove material where the extended thread would go and just use the existing thread.
You're screwed, literally. 
Area in red has been turned down to .810", that's how much of the pill extends beyond the threaded area in the head. I would like to cut the threads deeper so I don't have to mutilate the pill like that.
p.s. I must be losing it. How did I get 1.5mm from .050"? That's 1.25, not 1.5. Sheesh.
p.p.s. M22 x 1.25 tap is 3-4 times the price of a M22 x 1.5 tap...
Send it over and I’ll fix it up for you. 
Don’t do that. He’ll just use the pill and a pair of vise grips to cut the threads deeper. Send it to me, I’ll fix it real gud.
'It' is actually 'them', a whole bunch of them. Hence why I'd like a cleaner solution instead of hacking up the pills like that.
Is it worth dropping $40 on a M22x1.25 tap? Is that likely to work?
Is there anywhere you can take the pill to check thread compatability? If your doing a bunch having the right tool will pay for itself in Advil if nothing else.
Tough call. I’d suggest the threads will be sloppy.
stop denying comfy, it is painful to see you struggle with make-shift tooling, get it over with and get yourself a lathe somehow somewhere ;-)