It’s actually a 5/8-28 BSP (British Standard Pipe) thread, but a regular 5/8-28 will work. The BSP is 50 degree and the regular is 60 degree, I believe, but I could be wrong.
One of these?
Looks like I’ll have to find my other AA minimags somewhere in the house to chop as well. 
Not that it makes any difference from memory the thread angle was 55 degrees.
edeekeos, I cut the pill from a 1” diameter aluminum rod to fit the interior dimensions of the AA MiniMag. I attempted to make the light engine fit without getting into the threads of the light at all, but ended up cutting about an 1/8” into them so that the bezel would seat properly.
The top end of the battery tube did get cut down, so that I’d have a nice square bare aluminum contact surface to connect to the driver, as the twisty style would make this connection the “switch”. Doing this, I had to inset the spring a little deeper into the tail cap and take off unnecessary metal above the tail cap threads to allow the battery to fit properly.
Took some doing, but the light functions flawlessly now and is very easy to use one handed, going through the modes is a breeze.
Love this little light! It’s one of my favorites now.
Edit: Although you see bare aluminum inside the head, it wasn’t because it needed to be bored but rather contact with the cutting bit when I was seating the pill, cutting that 1/8” into the threads. It was a side effect, not a desired effect.
That listing says it's a 1/8".
-Garry
I’m only finding 5/8” x 14 BSP in my searches. Is that actually correct or is it really 28 tpi?
That is a hard to find item, so just use 5/8-28. Mine is a 5/8-28 NS. I got it on fleabay.
EDIT, they have one here. And on Fleabay.
Thanks Justin, appreciate that.
Woops, late night searching got me again.
That tap is just for the tail, correct? So that the tail cap can be screwed into the battery tube after it’s been cut down, am I seeing that right?
A more precise answer to your question would be that there are about 4 of the quick threads still showing in the head. Once the threads engage there is about 1 full turn to on. Easily keeping the 0-ring up inside the head for water tight operation, or as much as it ever was in that regard.
I cannot remove the pill, I glued it into the head with Arctic Alumina for thermal transfer and to keep me from messing with it anymore.
Edit: Perhaps some inspiration is in order…
Alot of good, and very helpful info in this thread folks. I appreciate it tremendously. Can’t wait to get the rest of my stuff in, so I can continue modding these little boogers! I have 5 mini’s here just waiting for some attention!!
I grabbed a 5/8-28 tap bit a few days ago.
For the life of me I can’t get this buggar to cut threads. It just cuts like a drill bit. I messed up the test run on the junk piece I chopped off, figured I took off a bit too much of the inside with the rotary tool. I went ahead and tried on the good section and it did the same thing even without relieving any of the metal inside the tube with my rotary. :~
I went ahead and just cut deep enough to fit the whole tailcap in and epoxied it into the tube.
Anyone ever have this happen, or know what I’m doing wrong?
To use a tap you have to use cutting oil and do short turns (1/8 at first, then 1/4 turn)then back off to clear the chips. If the axis isn’t true, it will strip out. If you cut too much(turn too far), it will strip out. Initially to start the cut you need to apply a bit of pressure along the axis or again, it will strip out. Starting with the right hole Dia is critical(hence the special drill bit first). Some practice is definitely in order before trying a Minimag.
Another method besides OL’s human lathe method is to cut the head and tail thread sections plus ~5mm ea along with enough of the knurled section to complete the tube length. These pieces get reamed out to slip over 15mm thinwall brass tubing and left a snug press fit at each end of the brass. This is how I made DBCstm’s AAA Minimag. It also makes it easy to add copper or brass rings at the seams.
Possibly your hole for the tap may of been slightly to small?
I guess I probably should have updated this thread sooner. Oh well. Anyway, I have been on a roll with these little suckers. The ‘Match’s 15min mod’ with the P60 pills has been working great(tightly wrapped in copper to ensure optimal heat transfer of course.) I also cut the threads down so the lights retain the factory length. I only have a drill press, and minor hand tools at my disposal, so all this has been winging it basically. I have pretty much got it down pat though. I have made quite a few, keeping some for myself, as well as selling to people at work, and gifts. Everyone gets a kick out of these, and most I show, want one. The ones I sell to ‘non-flashaholics’ use a 2AA single mode 800ma linear boost driver, and XML2 U2’s, that way they can just use whatever off the shelf AA’s they find. In any case, here are a few I have on hand:
The 2AA red one is an XML2 T6 3C on a Sinkpad, with a single mode buck driver, and 2x Sanyo UR14500P cells(0.85a), stock reflector & a UCL.
The 2AA grey one is an XML T4 7C same driver and cells(.90a) with a 60 degree flood TIR optic.
The 1AA red one is an XML U2 1A with a single mode driver, and an Efest 14500 IMR (1.7a), stock reflector, and plastic lens.
http://imgur.com/a/EIO4H/embed
I want to thank you all for the information and help I have gotten in doing these. Many people on this forum have been an inspiration for me, and have given me the motivation to attempt these mods. 
Very nicely done. Whats next on the modding for you? I sense that you need a bigger challenge now that you have these wonderful little lights down pat.
Haha, Thanks, yeah I have something in the works hopefully. I am waiting on a solid copper slug for a D Cell Mag, I snagged from here actually. My plan is an MTG2, with 5+amps. J)
with what Driver ?? i am aiming for a MT-G2 in 3D mag runing at 5Aor 6A