Hi GC. I just got done making a bong out of a Cabo Wabo bottle. The glass is like 1/4 inch thick. The stem is snug as hell. It is so amazing! I just got done with it, so I'll upload pics tomorrow when I am capable of doing it. EDIT: The hole took about 15 minutes to drill, but was well worth my time. The glass is so thick it actually supports the downstem while also allowing it to easily slide out while also being air tight.
def nicer and healthier than most homemade bongs, and I give you props on that, your next step should be trying to get it glass on glass
Always used an engraver for the liquor bottles, but thats a nice looking bore.. how did you drill the hole??