Well the guy had 33mm glass to hand, and said the play would be too much, even with cement/glue etc..... So we decided not to order the sapphire and go with mineral instead....
I am happy with what I received from him, it is a great improvement over the original marked glass, as I said before
At least if I damage the glass, I know I can get it fixed with ease
I would have preferred sapphire really, as it is a very hard material. However knowing my luck I would ding it one day and it would shatter!