How to Measure a Bowl or Downstem
Whether you're working with a vintage vase, ceramic cat, or glass thrift-store gem, getting the right downstem fit is key to airflow and usability. Here's a simple guide to measure the size you need.
What You’ll Need:
A digital or manual caliper (for most accurate measurements)
Your drilled hole (already cleaned and ready)
Bowl or downstem to test, if you have one
Step-by-Step:
Measure the interior diameter of the hole where the downstem will sit.
10mm = snug, smaller bowls
12mm = mid-range, versatile fit
14mm = most common size in commercial bongs
If using a downstem grommet (like a silicone seal), make sure to account for the grommet thickness when sizing.
You can test-fit using a pen shaft or similar round object before buying the real piece.
Quick Visual Reference:
Pencil = ~7mm (too small)
Sharpie = ~10mm
Marker barrel = ~14mm
Pro Tip: When in doubt, go slightly smaller. A tight seal can be expanded — a loose one will wobble or leak.