Darn, forgot all about this. Was caught up in firmware stuff. Hopefully I’ll remember tonight…
No worries, Thanks 
A few photos of the tailcap. The one on the left in all photos is the Banggood host, the one to the right is the Fasttech host. The light I built in the OP was the Banggood type but it’s no longer in my possession so I can’t check if it was exactly the same. I’d guess so though, I bought that host the same time as the one in these photos.
Thanks Mike. Mmm, mine had a different assembly, It did not have a screw in retaining ring, it was almost press fitted. I eventually broke out the press fit part and just gave up, it was messed up badly… maybe i should order from Banggood and try again 
Did you make the 2 little ‘grip holes’ in the fasttech tailcap?
Nope. The tailcaps in the photos are both completely stock.
I’ve found the switch that was in my version of this zoomie bought from Fasttech… It was just like that press fitted, no thread in the tailcap. Had to eventually break it out.
!http://manager.kaidomain.com/UploadFiles/635663245785599073.jpg !:http://www.kaidomain.com/product/details.S024076
No threads in the tailcap? That sucks. Seems like the designs of these things change all the time. When did you get it?
I think I still have the tailcap… will take a picture.
I’ve ordered it on 3 July 2015 from Fasttech