Received my two 18500 tubes today, fast shipping! Had to clean a little in the threads-in the same place on both, but easy to fix (as a former goldsmith I still have a lot of my old tools around). I´ve found that the stock (red) o-rings must be used on the tubes, not on the switch end of the light. If the red o-ring is used there then the extender will compress it so hard (tried with both-same result) that it will be pressed out of the grove unevenly and the extender cannot be screwed to bottom. Also, the tube borring is too small to take any but my AW 2200 mAh batteries, all my other 18650 batteries (and I have a bunch) just cannot be inserted in the double combination-maybe it will be better in the single 18650 extender, we´ll see (one on the way).