I'm looking into making myself a new bong. I already have a vase, but nothing else. Correct me if I'm wrong: I'll need a drill bit to make a hole for the female downstem to fall through the grommet, and a slider for the bowl. What size drill do I need to make a 12mm hole ( I that's how small the female downstems come, right?) and how much should everything including the 9mm slider and grommet cost?
You'll need a drill bit made to drill glass, not just a regular bit. Not sure about your other questions. Convert from standard to metric and you'll be fine.