title: How to measure a joint, and a downstem description: Tell a 14 mm joint from an 18 mm one with a dime or a ruler, check male or female, and measure a downstem the way it's sold. primary_query: how to measure downstem format: steps pillar: parts and fit updated: 2026-11-08
You need a US dime, or a ruler with millimetres. Two minutes at most.
1. Male or female
Look at the joint where the bowl goes. An opening with frosted glass inside is female. A frosted stub that goes into something is male. More on male and female.
2. A female joint: the dime test
Set a dime flat on the opening.
- It sits on top: a 14 mm joint. Its opening is 14.5 mm across and the dime is 17.91 mm.
- It drops in, about 9 mm down: an 18 mm joint. Its opening is 18.8 mm across, wider than the dime, and the walls narrow by 1 mm for every 10 mm of depth, so the dime wedges about 9 mm in.
Use a dime, not a penny. A penny is 19.05 mm across, wider than an 18 mm joint, so it sits on top of both sizes and tells you nothing. Coin sizes are from the US Mint; joint sizes from ISO 383 and the 1-in-10 taper of ground glass joints.
3. A male joint: the ruler
Measure straight across the frosted glass at its widest point, the end farthest from the tip.
| You measure | It's a |
|---|---|
| about 14.5 mm | 14 mm joint |
| about 18.8 mm | 18 mm joint |
4. A downstem: its length
Downstems are sold by the length of the part that hangs inside the piece. Measure your old one from the bottom edge of its frosted joint to the tip, and round to the nearest quarter inch (downstem size guide). Bring that number and the joint size to the bowls and parts shelf: downstems here come in lengths from 2 to 6 inches.
5. Then find the part
With the size and the kind, go to the 14 mm chart or the 18 mm chart. Every bowl and ash catcher in stock is listed under the joint it fits.