Pardon the profanity in this thread. What was pointed out with the threads? I just looked at the two pieces and I wouldn't call them square - they are maybe too fine for that, but the overall quality is pretty good. They feel great when threading, but of course I got Nyogel on them.
It was reported and confirmed by another member here that the Y3 battery tubes screw onto the HD2010 battery tube.
For flattening aluminium inside a cavity I flatten the head of a bold that is about half the diameter of the pill cavity (I have a block of cast iron that I made really flat that I use as a base under sandpaper, I use it for flattening led-boards too), wrap pieces of sandpaper around that and start sanding the pill surface with that.
I take mine to my lab for lapping. A little bacon grease on it and he’s really happy! 
thanks for the review
take a piece of broom handle or timber that fits in the pill + –3 cm
Take the center and drill a hole.
Take a drill of + –0.5 mm thicker and press it in the middle of the wood.
Now you can turn your drill machiene while the pill turned around to work for more flatter surface. sandpaper the edge at.
2nd way) turn the pill over and tap with a hammer and a piece spindle diameter of + –2 cm in the middle of the pill.
so that the center plane with the back side.
TomE: you have now one AR lens from flashlightlens.com ? for the y3
see you different on brightness?
penumbra, that makes me say “Well DUH!” I knew that! 
I’ve seen machinists go to great lengths to set up the machining of a part that takes minutes to do, even making components to facilitate this. I DO know that preparation is key to success. But I, like so many others, always look for the quick and easy way out. Not afraid to work, just afraid to use my brain apparently.
Thanks for that reminder.
problem with this methods is that you must have a little “technical mechanik ” feeling … :nerd_face:
Tom, you might try a variation of something I’ve done in the past. penumbra made me think of this and it should be simple.
I have used the double sided 3M emblem tape for cars, the stuff they put the Ford oval or Chevy bowtie on the side or tailgate with. It’s a thin foamy grey tape, sticky on both sides. A dowel or aluminum rod with this on the end, chucked into a drill or drill press, will enable you to turn that pill section like it’s on a lathe. You can then sand, rotary, file, scrape, however to get the turning pill flat on the surface. It’s most tricky to set the part gently on the adhesive and spin it slowly to test center, reposition til it’s turning true then press it firmly onto the tape. The stuff is quite strong, I’ve turned 7/8” copper bar stock this way to make a driver pocket in the end. This is also how I turn down a copper star. Turn it relatively slowly with my cordless drill and use a cut off wheel in the rotary tool to trim the star down. Takes a few minutes and works like a charm.
A piece of wooden dowel, like 1 5/16” clothes rod, can be shaped to fit inside the pill on a table saw, setting the saw blade for height so the round rod will be close enough to sand lightly then press fit in, once that end is done, the other end can be likewise shaped to fit into the chuck of the drill or table saw. I prefer the drill for it’s variable speed. Have no idea why I didn’t think of this before!
Thanks, Tom E. I've been thinking I may eventually attempt modding the Y3, but the E-switch part is intimidating. You make it look easy. 
I'm big on chucking stuff up to a hand drill too. I keep a variety of PVC couplings, pipe, and Phillip screwdrivers around just for that. But I have had bad luck trying to lap that way. Unlike a lathe where you have a fixed blade that moves across the surface that is turning at different speeds (Center material is moving past the blade slow, outer material much faster), the free hand sandpaper tends to dig in deeper on the outside of the pill landing. I always get a hump (and I don't mean the good kind) that way. So I prefer to manually lap my pills.
I'm sure I just don't know how to do it right. Hoping someone knows what I'm doing wrong.
Ohh - I ordered the single cell Y3's, so no extra tubes. Didn't try it yet - won't do me any good without ordering extras though.
Thanks for all the tips on working the pill top! Ended up though doing it same way as I always do, sand paper strip over the back end of a metal chisel - found it to be smooth and flat. I worked it extra with 150 GRIT more on the outside than the center, but don't think it did much - got a pic I'll post.
The OP has been expanded, adding tailcap assemble pics and details on modding.
Again I sit here admiring your modding skills Tom E. Orsm work on the driver and led.
Thanx! Few issues:
- I put a healthy nice dab of thermal grease and saw none squeezed out, so my rough test for flatness seems to have worked
- the stock big plastic piece seems too high - I get a black hole that goes away at bout 12" or so, but shouldn't really be there for a domed LED
- little disappointed in lumens and throw, but could be the centering piece, and also that I'm using a XM-L2 U2 1D which I've seen have less output than a 1A
- The light is pretty useless right now with the driver in a funky state - hope I didn't kill it
Wish I had pics or could recall what I did not on the fully modded Y3 I previously did a few months back... The reflector hole is an odd size I can't find an alignment piece to fit - something like 8.14 mm I believe. I'm thinking I cut the stock one back a lot, than filed it down - can't recall.
Tom, you can write an honorary chapter in the book Steve and I are Co-Authoring, the title is “Forget Me Not—-What did you say your name is again?”
Very nice teardown and mod as usual.
I like the idea of extending the soldering pads on the star with the small copper sheets, that way we can eliminate the soldering joint interference with the reflector base. Think this has been done by someone else before too.
I've done it before (copper sheet metal tabs), but pretty sure I've seen it done/posted about. In a surface where you have no room around the MCPCB, this won't work, but if you have the space, works well. O-L did the recent video about using these extensions, but put them over the wire holes in the MCPCB, then solder the wire directly to the bottom of the tabs, not the top. That method will work well for a HD2010 that doesn't have the extra space.
Sorry missed this Q. I believe I bought two a while back - one I used, one spare, so will update this light and test the difference. First time I posted the improvements measured - did pretty well, bout 5% or so. I also may try improving the focus - think it could be made better.
I’ve also cut the copper out from under the pad on the outer edge, soldered the wire to the bottom of the pad. Wasn’t easy, but….