I think it is 32mm
I don’t think MTN has the 3V 50.2
He said he is okay with a SST-40 which they do have on a 31.5mm board.
MTN does not carry 3v 50.2 yet.
The board may not be an exact fit.
I got a 32mm board from him with a 70 6500K mounted
I put it into a S70S, but it was very slightly too small for the screw holes to line up. So I had to mess with it to get the LED centered. But the centering ring holds it in place so it works OK.
Interestingly I put an L6 SMO into the other S70S, and it works great no donut hole. But it did not give a good beam in this light, went back to the OP which works awesome with the 70 (not .2). Just slightly less throw than the light with the 70.2 and SMO.
The board may be slightly thicker or thinner resulting in the beam difference. The LEDs APPEAR to be identical dimensions, but it may have to do with internals.
I have a spare star with a 70.2 6500K that I was going to reflow into this light, but I am happy with the current result.
Wow, I’ve learned quite a bit now, thank you all.
I had no clue the led is suppose to just sit (flow solder?) on the star/board with copper heatsink as 1 piece. I honestly didn’t know what I was looking at either 
Now I know.
I tested the board/star with a spare led from the leads it works, I turned it ~70% or so (guesstimate by lowest and turn it on, then holding it for a few seconds) the spare led was able to light up and this time it was quite bright.
now my options are
- replace the star w preinstalled led, easiest as it just requires me resolder it and call it a day
- try to find led and reflow it on the existing star/board, this is more difficult as it requires me to remove the star, reflow the led, then resolder it back on. All seems easy enough, but I’ve not done this ever.
Looks like mtn elec is OOS, but banggood has it and its an exact replacement, this is probably going to take a while to ship from china 
looks like a direct replacement
Just order the part. It is an easy fix.
And then use the bad part to learn to reflow!
Don’t forget you need thermal paste also.
Reflowing is lot harder than soldering plus we don’t know if he has the tools to reflow, probably not. Remember, he’s not an advanced modder, but a complete beginner. I was modding 2 years before I bought a hot air station and tried reflowing.
He can reuse the existing thermal paste as long as it’s not dried out and chalky.
I have done three reflows using a soldering iron I bought on Amazon for $29.
All have been successful.
When you are giving advice to people, it’s important you understand their skill level. If you look at ttylamg’s posts, it’s clear to me they are a very new beginner and don’t understand much about flashlights. I’m not even sure he/she can even solder, so I do not recommend they try something that is even more diffucult.
True, but that’s my skill level too!
Yes, all very valid approaches. I am taking a lot of short cuts, while mechanically inclined, I resulted in needing a lot of help. I don’t have basic skill or practice in this hobby, so I appreciate the guard rails for sure.
The reflowing video was very informative, but not something I would try just yet. I’ll wait till I accumulate more scrap part
That is why I suggested buying the replacement board you linked with the LED installed.
That only requires soldering two wires.
I suggest a good soldering iron, a helping hands (you can get that that at Harbor freight) and a solder tip wipe box.
Once you have the light working, you can use the same stuff to practice reflowing the LED on the board you remove, which is toast anyway.
I have had success reflowing using a soldering iron. I know that is not the preferred way.
Just keep in mind, if you remove an LED from a board and then replace it with an LED you took off another board, you don’t need flux or to add any solder to either part. In my VERY limited experience re-used parts have enough residual solder to just use heat,
YMMV!
I always replace the solder with fresh, high quality leaded solder. I also add extra flux.
You don’t know if enough solder was used from the factory plus you might loose some due to being stuck to the old led. If you have just a tiny bit too little you may not get good contact over the center thermal pad. It is the deepest pad. This can result in poor heat transfer and the LED burning up. It’s better to have too much than too little. Plus the old solder might be lead free which is harder to work with and requires higher temperatures.
The solder in liquid form can take just 10 seconds or so to burn off the existing flux, assuming there is any left in the original solder. There is no good reason to not add extra flux. It aids in the wetting action and helps the solder to flow.
Speaking of soldering, I know there’s google, but do you guys have a link to a good tutorial? I am basically learning by trial and error and watching only. I fixed items in the past but I really suck at it.
Check out this 3 part series from Dave at eevblog. Here is part 1.
These Pace videos are good, too.
Anyone ever think of making a bat signal cover for the fto3 got the idea when thick clouds were hovering low over our campsite
Finally got the replacement, of course I had to dedome it. I forgot to test it first before I start, now after dedome it won’t light up… just my luck.
Bummer. There is always risk involved in modding lights.
I think it’s a sign for me to explore reflowing. Now I just need to find sources of SST-40