Bong Blog: How To Measure Downstem Length & Joint Size

In this blog we answer all questions related to the main question of today: How To Measure Downstem Length & Joint Size? Is my bong 14mm or 18mm? This is essential to know when you're buying new bong parts such as downstems and bowls, so let's dive right into it.


What is a downstem

A downstem is the part of a bong through which the smoke enters the water. It’s a removable pipe that goes directly into the water chamber. Downstem is sometimes also called an adapter, a downpipe, stem, or tube.

Some bowls don’t have a downstem, or one that’s fixed to the bong instead of being removable. In that case, the only size that matters is the joint size (diameter) for replacing your bong bowl with a different bowl or even a pre-cooler or ash catcher.


Measuring a downstem

Measuring a downstem for your bong can be quite confusing. If you’re looking for a replacement downstem, you want to be sure that you’ve measured it perfectly so that the downstem fits your bong well and a good smoking experience is maintained. Although measuring a downstem can be confusing, it’s not difficult. Let us explain.

There are basically two measurements that matter: the downstem length and the joint size or “standard grinding”. Keep reading and we will tell you exactly what these are, how to measure them, and how to determine what size you need for your bong.


Measuring downstem length

Measuring downstem length is very easy, but you have to do it just right to get the perfect length. The length is measured from the top edge of the lower joint or “standard grind”. Have a look at the picture below.


how to measure downstem length


But I don’t have a downstem anymore, and now I don’t know what size I need to buy! Don’t worry, you can easily determine the size of the downstem you need by measuring your bong’s chamber. All you need for this, aside from a ruler, is a pencil. If you don’t have a pencil, a skewer or any small stick will work.

Stick the pencil into the bong where the downstem is supposed to go, and mark the spot where it sticks out of the joint. Then measure the part of the pencil that was inside the bong. You now know exactly how much space there is inside the bong. Then subtract about 1-2 cm or half an inch, and that’s your perfect downstem size.


measure bong downstem length with a pencil


Measuring downstem joint size

Below you can see how to measure joint size. This works for all bong joints or sockets, whether you're measuring the bong itself, the downstem, or a bowl. You always want to measure the top edge of the joint or standard grinding. So for an "inside cut" downstem or bong socket, you just put the ruler across the top part. Measuring a bowl socket is done horizontally, just as measuring the outside part of a downstem.

There are two main sizes for bong joints: 14,5mm (SG14) and 18,8mm (SG19). There are also smaller 10mm joints (SG10) sometimes used on dab rigs, and larger 29mm (SG29) and 45mm (SG45) that you see on the Blaze Glass Mix & Match bongs, but other than that, they are very uncommon.

As you can clearly and easily see, the (inside) diameter of the first downstem is about 14 millimeters (SG14), and the second downstem is about 19 millimeters (SG19).



The two pictures above show how to measure the inside diameter of a joint / standard grind. This lets you know what size downstem you need for your bong, or what size bowl fits in your downstem. Now let's measure the outside diameter of a downstem or bowl that we already have, so we can determine it the other way around.

It's clear that the first two downstems are both 14 millimeters (SG14), while the third picture (the bowl) has a diameter of 19 millimeters.



Measure bong joint size without a ruler

So, you're a real stoner, are you? Don't worry: we will show you how to measure bong joint size without a ruler. All you need is a €0,10 coin (10 eurocents) or a €0,02 coin (2 eurocents). The size of these coins is almost the same. Then put the coin over your bong socket / joint (at the top of the grinding, not the bottom). If the size of your bong socket is about the same as the coin, then it's SG19 (18,8mm). That's because a 10 cent coin has a diameter of 19 millimeters, and the 2 cent coin has a diameter of 18 millimeters. If your bong socket is smaller than the coin, it's most likely a SG14 (14,5mm). 

As we explained earlier, the two most common socket/joint diameter sizes are SG14 (14,5mm) and SG19 (18,8mm). The smaller and larger sizes are very uncommon.


Different types of downstems

Now that you’ve measured the length and joint size of your downstem, it’s good to know that there are different types of downstems.

Apart from the joint size, it is important to determine whether you need a male or female joint for fitting your bowl on the downstem. Luckily, this is very easy to see and/or remember: the male is the part that goes into the female part. So in most cases, the bong has a female socket/grinding, and a downstem with a male grinding goes into the bong. Then you place a bowl with a male grinding on the female upper grinding (or female inside cut grind) of the downstem. And in many cases, you can also swap male and female parts or use them together by using a male to female bong adapter.

Then there's the more technical differences: the best downstem material, a diffuser downstem or not, an "inside cut" downstem or one with two grindings... let's have a look.


Downstem with bowl or without bowl

There are some downstems with a fixed bowl, instead of a separate universal socket or joint for a bowl. These are usually cheaper and are mostly used on entry level bongs. In the first picture on this page, the last downstem (on the right) is a downstem with a fixed bowl. There's nothing wrong with this design, but it doesn't allow you to switch the bowl. This is especially important to note if you have a bong without a carbhole or kickhole, because then you want a bowl with a handle to lift it during your smoking session (because you don't want to burn your fingers touching hot glass).


Downstem with two grindings/joints/sockets

Perhaps the most common type of downstem, often seen on the simpler bongs, is one that has two seperate joints, with one basically sticking out of the bong for placing the bowl. On the first picture of this article, the first two downstems are of this type. One big advantage of this design is that you can use a downstem with an SG14 (14,5mm) joint that goes into your bong with the same size joint, and have the upper joint be of the bigger SG19 (18,8mm) type for corresponding bowls.


Inside cut downstem

An inside cut downstem looks a little more sleek than a downstem with two seperate joints, but it's basically the same. The difference is that the second joint is cut inside the first joint to save space, making it look like your bowl sits right in the bong without a downstem inbetween. It's called an Inside Cut Downstem because one grinding is inside the other.

If the outside diameter of an inside cut downstem is 18,8mm or SG19, then your inside diameter can never be of the same 18,8mm (SG19) type. There simply isn't any space for that. But even with an inside cut downstem you can use a larger diameter bowl, by using an adequate bong adapter. The most common type of inside cut downstem is one with an outside diameter of 18,8mm (SG19) that goes into the bong, and an inside diameter of 14,5mm (SG14) for the bowl.


Rubber joint downstem

The last type of downstem is a rubber joint downstem. We haven't spoken about this type of downstem yet, because on most modern bongs this is no longer used. The glass "standard grind" joints with universal sizes are just much better and give you much for flexibility. Nonetheless, they do work great and are easy to fix if any air leaks should appear. This type of downstem is often seen on older bongs and cheaper bongs, for example acrylic bongs. The corresponding bowl is often made of steel and attached with a screw thread. You may also see this type of downstem on ceramic bongs, silicone bongs or other small bongs that are mainly decorative.


Buying a new bong downstem

Now that you know how to measure the length of your bong downstem, it’s time to shop for a new one. Buying a new bong downstem is the most exciting part. We have all different shapes and sizes available on our website, so have a look at our downstems here. Be aware that you can upgrade your current bong by using a diffuser downstem – this makes the smoke much cooler and less scratchy. We also have indestructible silicone bong downstems for sale, so if you’re clumsy, that may be a good choice for you!


Some of the downstems available at Bongify


Looking for something else? Have a look at all downstems!

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