Thanks.
Yes, I mean o-ring. The ref has no shelf but the o-ring goes between the head and the ref. Glass lens is pushing the o-ring down from the top. Same way as in Jaxman Z1. Then on the top of glass goes the ss bezel which touches/pushes the glass lens directly.

Edit: The lens is fitted quite tight and tends to stick to the rubber o-ring beneath. This may cause some challenge to lift up the glass lens in order to take it out. I was clumsy enough to make a little Crack on the glass which can be seen on above picture, around 7 o’clock if you imagine clock’s dial.