I can unfortunately not tell you how these were made, since i had them made by a friend.
The important thing is to make sure the cavity that sits out toward the base and top is deep enough to sit over the stem leftovers, and of course that the glass tube fits in the hole. I had them made in stainless steel, since there is a good chance they will be exposed to water and other fluids over time. I got 4 identical, but as mentioned the hole was to big, so i had to put in an aluminium sleeve inside. The aluminium tube was chamfered to approximately fit the angle of the steel cup. This was done by simply filing and sanding it down.