I ordered two of these C8 extension tubes from FastTech.
I just thought I’d post my findings in case anyone is interested.
They fit the Convoy C8 and the Wallbuys XinTD knockoff, but not the Tmart Tangsfire C8.
I didn’t bother trying it on the IOS XinTD, because it would looke silly with back and grey.
It didn’t fit the Lightmalls C12, but I found that light to be very poor quality and am awaiting another from a different source. I’m curious to see if it will fit that one.
Cool! I've been looking for these! Thanks for sharing. I have a few that I bought from eBay last fall but that source has since dried up.
Awesome. Now my uninitiated question (as I just ordered two) is; what do you do driver-wise to handle the extra voltage?
Good question. I haven’t even thought about it. Right now all I can think of is a Zener modded Qlite.
Anyone?
I ordered some of those Feb. 2, and got a message from FT that their supplier sent the wrong tubes. They shipped the rest of my order Feb. 16 while they waited for replacements.
During packaging, we discovered that the item SKU 1575200 we were about to ship you is with a little problem, the supplier has provided the wrong stock to us. To avoid further delay, we have shipped you everything else except this item. We will have it replaced and shipped to you as soon as possible.
It will be shipped with a separate tracking number and we'll e-mail that to you when it ships.
Tubes shipped Feb. 19. I'll let you know what shows up. 
Do you know if it will work on the cheap Ultrafire C8s?
I’ll let you know when I get home. I just started working on a cheap Ultrafire C8 today.
I have some of those FT extensions, they don't fit any of the standard C8s I own (around 7-8 lights, they all share the same thread size/pitch on both ends of the battery tubes, the extensions don't fit anywhere on any of them).
Will these extensions fit a Convoy M1?
They don’t fit a Convoy M1.
It fits my cheap Ultrafire C8, but there are so many out there, it’s a crapshoot.
Because of the oddities between male & female threads the extensions will screw onto the battery tube and seat before the different threads bind up, but the tailcaps will not screw onto the extensions more than about 1/2-3/4 turn.
I got mine, same as Ouchyfoots. They look to be made by the same factory that makes the Convoy C8, perfect matching finish and knurling.
Add 2 extensions and maybe a sleeve and you can run on 4 AA's, handy in long blackouts or if you don't want to keep li-ions in the car in summer.
Great idea!
I got the FT extension in yesterday, and it sure does fit and match up well with the Convoy C8's, but nothing else so far.
4 AA ? 1.5X4= 6 volts, nanjc 105c driver have 4.5 volt max. Maybe you meant 3 AA that do 4.5V.
3 AA is a great idea, someone tried it ? The batteries are the correct lengh ? Good runtime ? This would make a nice alternative C8 for a gift.
Hang on, 4 AA's might be too much voltage for some C8 drivers. I have a C12 on 4 AA's but maybe voltage sag on high is keeping the driver alive.
Someone who knows what they're talking about, please chime in!
Maybe use 3 AA's and a dummy cell to be on the safe side until verified as safe.
Have you ever tried it? Despite what the datasheet says they run just fine from 6 volts (open circuit - of course once switched on it will be less than that).
For example: http://illuminationsupply.com/led-drivers-c-52_32/8xamc7135-304a-selectable-mode-driver-p-142.html
"Input Voltage: 2.8-6V"
Standard everyday ordinary Nanjg 105C hardware. It works fine.
I just built two lights using those drivers and I’m running them with 2 x 3V CR123 cells. They’re running just fine.