From the third pic from the right at fasttech it shows a retaining ring in the bottom of the head, its possible this fits a 17mm driver.
Nkresho can you check the measurement to confirm that.
Wait a minute he said he has a mtn (17mm) boost driver in it now, so yeah 17mm fits.
I put a mtn boost in a convoy m1. Before that had zener 2x18350 fet. Used a 70.2 and a step drill bit to open reflector. Gave it away as a gift but i really liked it.
Nope, mine won’t fit a 17mm driver. It actually falls through the aluminum retaining ring. I used a 17-20mm adapter inside a 20-22mm adapter.
You could also try a Nichia 144AM build
Thanks for letting us know nkresho. It will fit just needs two adapter rings. 
Just to give some perspective to just how tiny this temp sensor is I took a pic with a 7135 laid out beside the temp sensor, most people know about how small a 7135 is. I can’t even see the reference dot without magnification. I held the actually board up to my screen and measured the width, this pic seems to be about 7 1/2 times bigger than the actual size. Split that temp sensor in to about 7 parts across 7 parts up and down, take just one piece, and that should give about the actual size.
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Made a copper stud for the driver for a better less resistance connection.
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Mr. Moderator007, thank you very much for advice!
I do not have same skill as you have or copper wire, so I use a cable terminal and shape it to fit. Size is 5mm long and 4.5mm wide.
Tip to beginner - I use needle-nose plier to open and close brass ring. It does not fit well so I made a lot scratches, so I recommend getting thin-tip pliers to open and close retaining ring. What method do you use?
My gxb172 is Working! 
Congrats!
I use these:
And filed the tips down to be even smaller.
Thank you! Do you recommend straight nose or bend nose to be easier to use?
I have the straight version and it works fine. Though I do have a nice stiff hardened steel pair of curved tweezers I have used to screw/unscrew pills and rings. I use those a lot then do the last bit of torque with the above pliers just cause the tweezers are less bulky and I can use them for more things.
A tip for installing this driver in a S2 pill.
Capacitor C15 when installing the original ring will hit the ring. You can take a round file or convex file and file around the inside of the ring for clearance of C15, filing changing the angle on the ring from the top to where the ring contacts the driver. Try not to take material around where the ring connects to the driver. C15 is the only component that is anywhere close to the ring. Filing clearance, eliminates the need for a added copper wire around the driver ring.
I would suggest something like this for $5 to $10 locally.
You can use the tips without the pliers to get good twisting torque. Plus you can both squeeze or push apart the tips depending on the type of bezel you have. They are the flashlight modders best friend. 
While we are on pliers, this is the pair I use for rings and pills. It will reach down the entire length of a 18650 tube light to get to a pill. I had one light long ago that was basically a tube with a tail cap, no separate battery tube or head with threads. I bought something similar to these to get the driver and led out to mod. The snap ring pliers above also work very well for getting tight or glued rings or pills out.
https://www.amazon.com/SE-LF01-Professional-Quality-Needle/dp/B001BQF1AQ/
I’ve got a set of similar pliers as well. I don’t use them that often, but they are a nice thing to have in the flashlight “toolkit”.
Post here to show my result of Gxb172 build. Detail of my progress was on my thread here: https://budgetlightforum.com/t/-/54909
First, many thanks to schizobovine and moderator007 for their motivation for building Gxb172. It was a little challenge to build driver but the result is worth the effort. Also thank you for the tips and suggestion for building the driver to make my build easier. Finally thanks to loneoceans for creating such amazing driver. I never expect 17mm driver to actually be able to run at 50 Watt.
schizobovine, I notice you say that you do not need to program fuses, but the firmware need fuses to program, such as CLKDIV8. Maybe this cause your driver ramping and temperature to be effect?
Photos:
Beam on wall with XHP50.2:
Low mode:
Outdoor with clear air no fog, on turbo (light is extremely bright) - at 5A setting, now I change to 5.5A.
Observation after few day:
After using flashlight for few day, here are my observation:
- Flashlight is extremely bright! I solder jumper to enable 5.5A maximum turbo. Single flashlight is enough to light up entire room!! I have never seen such small flashlight to be so bright.
- Lowest mode is quite dim (good), useful during night time without be too bright for night-vision.
- I notice flashlight has very-very short bright flash during turn on, but only during dim modes, likely not problem.
- Flashlight get hot extremely quickly! It seems thermal control works well, and automatically dim light about after a minute, however, thermal control will also increase brightness (all the way to maximum!) if you cool flashlight (such as when put in cold tap water!!). So in cold weather, I think it can stay very bright for longer time.
- Although front get very hot, flashlight body is still ok to hold.
- I did not notice thermal 'turn off' or any high frequeny sound as report by schizobovine. Moderator007, did not notice high frequency sound also. The flashlight is silent at all modes.
- XHP50B beam is nice in the middle but slight yellow/green around center hot spot. Maybe Nichia LED will be better?
- Mode memory is simple and working.
- So far tail-switch with wire bypass is still working, but I don't use turbo mode for long time.
- Regular mode brightness is quite useful, no need to change.
I have not encounter any flashing error code yet. I hope to do more simple test soon, such as with low battery.
Current Measurement:
For low values, I use multimeter in Amps setting. For turbo mode, I use wire and extech clamp meter (but 2.5% error+some digits). Battery used is LG HG2. I also solder J1 and J2 to test turbo mode at 5.5A. Default turbo mode is 5A. According to Loneoceans current chart of current to 6V LED, here is the tail-cap current I measure:
- Moonlight (<10mA) - 12mA
- Candle (no rating) - 20 - 40mA? Jumps around
- Low (50mA) - 72mA
- Med (250mA) - 390mA
- Bright (1A) - 1520mA
- Turbo (5A) - 11.2A (clamp meter)
- Turbo (5.5A) - 12.4A (clamp meter)
Be careful - tail current only applicable to my battery, if you use better battery, current may be less. It seem like with changing resistor or firmware, much more current can be achieve!
However at 4V battery voltage, 12.4A is already 49.6 watts!!
Sorry I have no equipment to do lumen measurements. Will need to use moderator007 measurement.
Review:
Overall this was very interesting project to solder. Although I have soldering experience, Gxb172 was still difficult to solder together, but easier with practise. I recommend using usb microsocope or magnification during soldering, very small solder tip, very thin solder wire, and hot air. For mistake, thin solder-wick is the best.
I also suggest using flux pen and needle tweezer. For cleaning, I use cleaning alcohol and cotton swab. Solder for temperature IC is most difficult because it is very small, so I suggest using no solder, only flux. High heat and low air speed. Inductor is hard to solder, but just keep at ~270C air heat for a while and it will solder.
Finally, before assemble I suggest to test with multimeter to make sure no shorts, then test before putting into flashlight host.
For program, I don't know of easier way than using pogoprog, but you can also use thin wire soldered to programmer. I use Atmel ICE, so I have no idea about USBASP, but moderator007 has used it to program so it will work.
Difficulty - 7/10
Cost - 8/10
Brightness & result - 9/10
I hope to be able to get firmware to change for even more current, or I may have to do resistor mod like moderator007 Hopefully now other people here can also make their own driver.
It seems the C3 and C4 capacitors that’s recommended for this driver are back ordered almost everywhere.
The last ones I purchased I had to buy from TTI for a premium. Any body know where they have these reasonable in stock.
I’m just wondering why their selling out everywhere. Does it mean there’s more people building this driver than we know or just coincidence.
I can’t even find suitable replacements in stock at my usual suppliers. 
For the caps, you can order them on Mouser:
https://www.mouser.ca/ProductDetail/TDK/C3216JB1A686M160AC?qs=sGAEpiMZZMsh%252b1woXyUXj9l5PHLyix2ViFOKbgN0rsI%3D
It’s not the ones recommended on the right, but they will work with 6V emitters.
If you can wait, perhaps we can bulk order together so we get a 20% lower price, as I’m planning to make some buys too.
If you want something that will work well for medium power operation(not exceeding 30W), and willing to wait a bit, here’s one similar:
I’ve checked the datasheet, and except for the capacitance, everything checks out.
The 10v version I can find but the 25v is what I have been using and is what seems to be drying up.
I think I saw a 33uf 16v version on my search somewhere and maybe what I end up going with.
I’m going to try a xhp35.2 someday with this driver so I’ll need 16v or higher with it. Seems kind of counter productive though making less lumens but I guess more throw.
Did you see the 2nd link? It seems to have the same characteristics, except for higher capacitance.