I may be wrong but the mcpcb says xp. So in mm guessing it’s just a standard Cree xp footprint
I’m use this one in the Courui D01 + XHP35 (Sold Out Currently!)
S, I did do some research on the XHP35's and can only conclude they are true XP footprints, compatible to all our XP MCPCB's. However with the stock PK26, there's no specific info provided on the LED, so who knows what the true "Minimum luminous flux group" or bin is (ex: D4, E2, E4, etc.). Best thing to do is buy one from MtnE, so at least you know. But Richard doesn't post the order code, so you don't have all the information, such as CRI spec, which would be nice to know.
Also, his top bin XHP35 is an HD at E4, but his spec on output is 600+ lumens @350 mA, so it's vague.
The CREE data sheet has been updated from Rev 0 to Rev 1 sometime in 2016. Mouser has Rev 0 posted, while at the CREE website it's Rev 1. The lumens ratings @ 25 C have been updated to lower values:
Lumens @350 mA and @25 C
D4: from 621 to 612
E2: from 666 to 656
E4: from 717 to 706
It appears the HI's highest bin is listed at D4, so MtnE's E2 is above the chart, but that's fine - same thing for the XM-L2 U4's.
In how it looks, the bin codes could make a pretty big difference in output of an XHP35, but the CRI generally drops as the bin code goes up, so it's all a tradeoff.
Cool, on all counts. 
Yep, XP-G2 board for the XHP-35, anything that’ll take an XP-L will also take the XHP-35.
And yeah, gunning for top output leaves the High CRI aspect behind.
Keeppower 26650 dont fit well.
Extension tube too short . Clearly not a finished product.
I am very distressed by this . Need another tube . Or the back cover
Unfortunately it's very fussy/limited on 26650 sizes - the LiitoKala fits fine in mine, and I consider it the best 26650 battery on the market, plus one of the cheapest from GearBest. I mentioned this limitation in the OP under cons.
I understand why there are no springs. In turbo mode, the battery current is very large (7-9A). It is necessary to shunt spring. Or make direct contact with the cover. And with the driver. But it was possible to make the cover of another form.
In “DQG 4th tiny 18650” the cover overlaps part of the thread - it is not visible. When put long batteries.
http://forum.fonarevka.ru/album.php?albumid=1062&pictureid=15178
Unfortunately here the developer did not think of this
Looked at the picture and agree - a tail design like that would hide the issue, but the tail assembly would be wider than the body, and the lip would have to very thin to not look bad. It works well for the DQG - not sure if it would work well for this light.
RIC himself is not happy with all the issues of this light. The cons on this light are significant.
Keeppower 26650/5200mAh
we have been able to get it to work with a 26650.
Are all your thread sections tightened down? Not sure but do i see the O-ring showing at the tailcap?
It’s work.
Battery is backward in the top pick……yes it works…but all the sections cant be tightened down….mine works with a keeppower cell also but i cant tighten down all the sections.
The best thing to do is to tighten the cap. At the same time loosening the extension tube of the head. Then it does not look so ugly. But still visible O-ring.
I want to make a Al washer. And put between the driver and the extension tube.
Yup thats what i do….this light just always seems to just sit in my closet.
Why not to buy batteries which fit the lamp? 
LK cells are so cheap, high capacity, great performance - there's no reason at all to try anything else in this light. It works, and it works well. It seems like they designed this light for that cell. I've been very happy with mine. I even invested in 7 trits, installed them last night. The biggest issues I have is the bright flash for low, and that low isn't low enough. The UI is decent enough - click&hold is pretty quick.
I've been finding the button "glow" to be useful. Using the light in darkness, it's easily visible. Was hoping the trits were brighter, but this is my first experience with them. I chose yellow - bought from BangGood.
I have the LK cells coming but they have been at the port of los angeles since Aug 17th. I am 60 miles from los angeles.
Thanks for the reviews. I heard that it is “very annoyed that it flashes on turbo when you turn it on to low”, so is that true?
yes