18mm vs 19mm: They're the Same Joint

Short answer: yes. An 18mm bowl and a 19mm bowl fit the exact same joint. If your bong takes one, it takes the other.

Why are there two numbers for one size?

Because brands round differently. The joint itself measures about 18.8mm across. Some makers round that down and call it 18mm. Others round it up and call it 19mm. Same piece of glass, same ground-glass taper, same fit — just a different number on the label.

This goes back to how glass joints are standardized. In lab glassware, this size is known as a 19 joint (a 19/22 or 19/26 taper). The smoking world mostly calls it 18mm, but plenty of brands — GRAV is a well-known one — label it 19mm. There is no separate "18 joint" and "19 joint." There is one joint, with two names.

What fits what

• An 18mm bowl fits a 19mm downstem or joint, and a 19mm bowl fits an 18mm downstem or joint. They are fully interchangeable.

• The same goes for bangers, nails, and ash catchers: if it says 18mm or 19mm, it fits the same joint.

• One thing still matters: male and female have to match. A male piece slides into a female joint; a female piece fits over a male joint. Size being the same doesn't change that — an 18mm male bowl still needs a female joint to slide into, whether that joint is labeled 18 or 19.

How to check what size you have

If your old bowl or downstem has a number on it, that's your size — 18 or 19, same thing. If there's no marking, measure across the joint with a ruler. A quick trick: a US penny is just over 19mm across. Set it on top of a female joint. If it drops partway in and wedges, that's the 18/19mm joint. If it sits about flush, that's a 14mm joint instead.

What is actually different: 14mm

Don't mix up 18/19mm with 14mm — that one really is a different, smaller joint, and the parts don't swap. A 14mm bowl will sit loose and leak air in an 18/19mm joint, and an 18mm bowl won't fit a 14mm joint at all. If you need to run a 14mm piece on an 18/19mm joint (or the other way around), that's what an adapter is for.

The takeaway when you're shopping

When you're buying a replacement bowl, downstem, or banger, don't sweat whether the listing says 18mm or 19mm. If your piece is either one, both fit. Buy the piece you like, in the style and color you want, and it'll seat the same way.

Questions about what fits your piece? Bring it by the shop or send us a photo of the joint and we'll help you match it.