So I finally got around to submitting a claim with Banggood for the S41s with tubes that don’t fit properly. I can’t see how I can submit a video though, I use Imgur and it doesn’t seem to accept video. Can anyone enlighten me?

Meanwhile these are the measurements of the thread areas, it seems the threads inside the head are flattened out, which is probably what is causing the problem.

inside head 21.7mm
outside 18350 tube 21.75mm
outside 18650 tube 21.7mm

Looks like even the tube that fits is only holding on by 1/20 of a millimetre, not good!