You use two of the sections with the ten ribs. Those sections have one male and one female thread.
With the #3 and SK68, the male thread fits into the zoom flashlight body in place of the tailcap.
So you can stack two of the “11-rib” sections, and you use the zoomie tailcap.
(in that case, you have the other battery tube section, tailcap, and emitter as a poor 1AA flashlight)
Or you can stack the one 11-rib section with the other section and keep the “3W” tailcap.
I guess this needs a picture, I’ll get one showing the variations.
With the Cofly zoomie, the female thread fits the zoom flashlight body in place of the tailcap, and you keep the “3W Police” tailcap switch, which has a female thread.
(in that case, I forget if there’s any way to use the leftover parts.
For a few years I had no problems; the last few #3 zoomies I tried had incompatible female threads though, so the extra section wouldn’t fit.
I can still find #3 zoomies for $2 intermittently, on sale at AliExpress (last ordered some a week ago though the price bounced back to $4 as of right now)
Not sure if they’ll have compatible threads til I have them in hand to try out though.
All convoy S series have same threads. Simon sais that short tube wont fit only because different length of tube over threads (18350 tubes were made for S2+ so they fit S2+ and probably S3).
Hat tip to t18, at: Semi groupbuy Jaxman X1 host - #29 by T18
Jaxman X1 and Convoy L2 half tube extension lego (9 pictures somehow presented page-by-page in a single window in a single response, lovely)
I have a blue tube sold by Banggood (US warehouse) for the S2+ and it fits and works perfectly on the X2R and the S2+.
I have a second blue tube, also sold by Banggood (CN warehouse) for the S2+ that also works on the S2+ but does not even thread into the X2R.
I have a black S2+ tube directly from Simon, it also does not thread into the X2R.
I now also have a black tube sold by Banggood (CN) as “Eagle eyes 18350” linked earlier in this thread. It threads into the X2R perfectly but does not work correctly. I believe one end is not long enough to reach the contact shelf in the head. Also, the threads on this one are very very shallow, as in the ridges themselves are about half the height of those on the Convoy tubes.
Mine arrived yesterday, I had ordered two of these (maybe I ordered the wrong one?) but neither of them match the threads on any of my Convoy tube lights. Also, even though they are both supposed to be the same SKU, they don’t match. The threads are the same, but the machining is slightly different, and the finishes are much different between the two. One is a nice matte finish while the other has a shiny sheen to the anodizing. Kind of like buying two different 501b hosts from two different vendors…
At a minimum, the latest VG10 tailcap legos with the ThruNite TC12 V2. The tailcap innards swap between the caps too. Will check for other swappable parts and post some pics.