Hi All - I got some new tanks, glass whatever, and the mouth piece end fits perfect, the top piece you stick in your mouth but the bottom won't pass over the very last piece of metal ring and then there's the circle slot for the glass to slot into. The glass is too small to go over it. It was purchased as 21mm and looks exactly the same as the glass cylinder that comes with the innokin TC100 Subv. The original glass sure doesn't look tapered. I'm sure I'm doing something wrong but I've tried for a few weeks now and I haven't got a clue. Please help.............thanks Mal