undefined | Deep End

title: 14 mm or 18 mm bowls, and which fits your bong description: What the 14 mm and 18 mm on a bowl actually measure, why one won't fit the other, and every bowl in stock in each size. primary_query: 14mm vs 18mm bowl format: depth chart pillar: parts and fit updated: 2026-11-08

Called	Measures at the widest point	Bowls in stock	Pieces here with this joint
14 mm	14.5 mm	30	49
18 mm	18.8 mm	8	0

The names are rounded. Glass joints follow the sizes used for lab glassware, where the standard list of joint diameters includes 14.5 mm and 18.8 mm, measured at the widest end of the male part (ISO 383). Water pipe makers call them 14 mm and 18 mm.

They don't mix

A 14 mm bowl is too narrow to seal in an 18 mm joint, and an 18 mm bowl won't go into a 14 mm one. Both joints taper by 1 mm across for every 10 mm of length (ground glass joints), so a smaller part slides too deep and wobbles, and a bigger one stops at the rim. Match the size first, then male or female.

Which one do you have?

Of the 49 bongs and bubblers here with a listed joint size, 49 use 14 mm. On this shelf, 18 mm shows up on bowls and ash catchers. If your piece came from somewhere else, the dime test tells the two apart in a few seconds: a US dime drops into an 18 mm female joint and sits on top of a 14 mm one.