Most people don’t think about their downstem until they have to replace it.
Then, suddenly, it becomes the most important part of the setup. You measure your joint size, guess the length, buy a new one, and—if you get it wrong—you’re stuck with something that either doesn’t fit, clogs airflow, or barely reaches the water.
A properly sized downstem isn’t just about making sure it fits your bong.
It directly impacts your smoke quality, airflow, and cooling efficiency. A too-short downstem won’t diffuse properly. A too-long one will hit the bottom of your bong, restricting airflow. And if you’re not using the right joint size, expect air leaks that dilute your hits.
So, how do you get it right?
-
Measure joint size accurately—guessing doesn’t cut it.
-
Find the correct downstem length—not too short, not too long.
-
Understand how downstem shape and percolation affect airflow.
This guide covers everything: how to measure your downstem, the difference between 10mm, 14mm, and 18mm joints, the impact of slits and percolation, and even which materials hold up best over time.
Making Sense of Downstem Sizes and Measurements
When choosing a downstem, size matters in two key ways.
- Joint diameter
-
Length.
Get either one wrong, and you’ll be dealing with air leaks, poor percolation, or a completely useless downstem.
Downstem Joint Sizes Explained
The most common joint sizes are 10mm, 14mm, and 18mm. This refers to the diameter of the joint connection point between the downstem and the bong.
Here’s how we measure our bong’s joint size:
-
Use the penny trick: A penny fits halfway into an 18mm joint, barely fits into a 14mm joint, and won’t fit into a 10mm joint at all.
-
Measure the inner diameter of your bong’s joint with calipers or a ruler.
One question we hear every day is, “can I use any downstem, or does it have to match my bong exactly?”
Answer: Your downstem must match your bong’s joint size exactly—an 18mm downstem will not fit into a 14mm joint, and vice versa. However, if your downstem has a different inner joint size, you’ll need a bowl that matches it (e.g., an 18/14mm downstem requires a 14mm bowl).
If you want to use a downstem that doesn’t fit your bong’s joint size, adapter fittings exist to mix and match sizes.
How to Measure Downstem Length Accurately
Downstem length is measured from the bottom of the frosted joint to the tip—the part that sits in the water. Use the pencil trick: Insert a pencil into your bong’s joint, mark the depth, then measure it.
“What if my downstem is too long or too short?”
If it’s too short, it won’t reach the water—wasting filtration. Too long, and it hits the base of the bong, restricting airflow. Getting this right is key to maximizing smoke diffusion.
Figuring Out the Best Downstem for Your Bong
The right downstem does more than just fit your bong—it optimizes airflow, enhances percolation, and improves cooling.
Whether you’re replacing a broken one or upgrading your setup, understanding the differences between fixed and removable downstems, downstem length, and airflow considerations will help you make the best choice.
Fixed vs. Removable Downstems
Not all bongs use removable downstems.
Some stemless bongs have fixed, built-in downstems that connect directly to percolators inside the chamber. These designs eliminate the need to measure downstem length but reduce customization options.
Removable downstems are more common and offer flexibility for customization and replacements. If you own a beaker bong or straight tube, you likely have a removable downstem that allows you to swap for different lengths, percolator styles, and materials. This customization can significantly affect your smoking experience.
If you prefer easy cleaning, a removable downstem is the better option.
Fixed downstems require deep cleaning techniques like alcohol soaks and pipe cleaners, whereas removable downstems can be quickly swapped out when buildup occurs.
How Downstem Length Impacts Smoke Quality
The length of your downstem determines how much cooling and filtration your smoke undergoes before reaching your mouth. A longer downstem allows smoke to travel through more water, cooling it down further.
However, if the downstem is too long, it can hit the bottom of the bong and restrict airflow.
Shorter downstems offer less diffusion but allow for quicker, more direct hits. They are ideal for smaller bongs and users who prefer stronger, less filtered rips.
Beaker bongs usually work best with longer downstems because they allow more room for the smoke to travel through water, while straight tubes tend to require shorter downstems for optimal function.
Wide vs. Narrow Downstems: Airflow Considerations
The internal diameter of a downstem affects how much smoke and air pass through at once.
A wider downstem provides less resistance, allowing for bigger, faster rips, but it may not filter smoke as effectively. A narrower downstem increases resistance, creating smoother, more controlled inhales.
If you want more percolation, a diffuser downstem with slits or holes can help. These designs break up the smoke into smaller bubbles, increasing filtration and cooling. However, more diffusion means more drag, which can make inhaling slightly harder.
Customers love our TAG - 18/14MM Open End 32 Slit Multiplying Rod Bong Downstem. This has plenty of slits allowing for a smoother and cooler draw. The percolation is off the charts with this one!
“My bong bubbles poorly—does my downstem affect that?”
Answer: Yes, the right downstem length and style significantly impact how well your bong bubbles. If your downstem doesn’t reach the water properly or has too few diffusion slits, it won’t create the small bubbles needed for effective cooling and filtration.
Make It Bubbly: Downstem Types and Percolation Styles
If you’ve ever hit a bong that felt way too harsh or one that bubbled like crazy but didn’t hit as hard, chances are the downstem was the reason.
Understanding the different types of downstems—and how they affect airflow—can completely change your smoking experience.
Diffused vs. Open-End Downstems
A diffused downstem has small slits or holes at the bottom, breaking the smoke into smaller bubbles as it passes through the water. This increases surface area, cooling the smoke more effectively and providing a smoother hit.
The more slits or holes a downstem has, the better the diffusion, but increased diffusion can also add drag, making pulls feel more restricted.
An open-end downstem is a simple tube with no diffusion slits.
Smoke travels through in one large stream, creating fewer bubbles and less filtration. While this can make for a harsher hit, it allows for larger, faster rips with minimal airflow resistance.
Percolator-Integrated Downstems
Some downstems include built-in percolators to further enhance smoke filtration. Popular styles include:
-
Tree percs – Multiple thin arms filter smoke through tiny slits, offering excellent diffusion but requiring more effort to clean.
-
Showerhead percs – A circular design with vertical slits that provides even, controlled diffusion with minimal drag.
-
Honeycomb percs – A disc with many small holes that creates hundreds of tiny bubbles, maximizing filtration while maintaining airflow.
Using a percolator-integrated downstem can improve cooling and filtration without requiring a separate perc in your bong.
Downstem Materials: Glass, Metal, or Silicone?
Some smokers want the cleanest possible flavor. Others prioritize durability. And then there are those who just need something that won’t break after one bad drop.
Your choice of material affects not only how your bong hits but also how long your setup lasts.
Borosilicate Glass: The Best Choice
Most downstems are made from borosilicate glass, and for good reason.
It’s heat-resistant, easy to clean, and preserves the natural flavor of your smoke. Glass downstems also come in a variety of percolation styles, from simple open-end tubes to multi-slit diffusers.
The downside? Fragility.
Drop a glass downstem on a hard surface, and it’s probably done for. Even high-quality borosilicate, which resists minor shocks and temperature changes, won’t survive a nasty fall.
If you’re careful with your gear and want the purest, unaltered flavor, glass is the way to go. But if you tend to be a little rough with your bong, you might want something more durable.
Metal Downstems: Built to Last
For smokers who prioritize durability over purity, metal downstems offer an almost indestructible solution.
Made from titanium or aluminum, like the Titan-Stem Diffused Bong Downstem. These downstems can handle drops, bumps, and years of use without cracking or breaking. Some even have adjustable lengths, letting you fine-tune how deep your downstem sits in the water.
But metal isn’t perfect.
It absorbs heat, which can make hits feel harsher, and some smokers notice a slight metallic taste over time. While high-quality titanium minimizes flavor interference, it’s still not as clean as glass.
Silicone Downstems: Flexible and Travel-Friendly
Silicone is the wild card in the downstem world.
It’s nearly unbreakable, bends instead of shattering, and works great for portable bongs or clumsy smokers. A silicone downstem can be stuffed into a backpack, dropped repeatedly, and still function perfectly. It also stays cool to the touch, unlike metal.
The trade-off? Flavor retention.
Over time, silicone absorbs odors and flavors from previous sessions. Even with regular cleaning, that rubbery aftertaste can become noticeable. Some designs include a glass or metal insert, helping to preserve flavor.
Turbocharge Your Bong with the Right Downstem
Sometimes, the problem isn’t your bong—it’s your downstem holding you back.
A simple swap can completely change your smoking experience, giving you better airflow, smoother hits, and enhanced filtration.
Whether you’re looking to improve diffusion, add an ash catcher, or just make sure your setup works as efficiently as possible, upgrading your downstem is one of the easiest and most effective ways to level up.
Matching Your Downstem to an Ash Catcher
Adding an ash catcher keeps your bong cleaner and adds an extra layer of filtration, but you need to make sure everything fits correctly. Your downstem should have the right joint size and length to accommodate the added piece without making your bong unstable.
Many smokers make the mistake of choosing an ash catcher without considering how it affects the downstem. If the angle is off or the weight distribution is poor, your bong can become top-heavy or awkward to use.
Using Adapters for a Perfect Fit
Not all bongs and downstems are naturally compatible.
If you’ve ever found the perfect downstem, only to realize it doesn’t fit your bowl or bong, an adapter can save the day.
Common adapter types include:
-
18mm to 14mm reducers for using a smaller bowl with a larger downstem
-
Male-to-female adapters for making different joint types work together
-
45-degree or 90-degree adapters to adjust angles for better function
These simple add-ons can prevent air leaks and make your setup more versatile, letting you experiment with different downstem styles without being locked into a single size.
Replacing a Stuck or Broken Downstem
A stuck downstem is a common problem, especially if resin buildup or glass expansion from heat traps it in place.
To remove a stuck downstem:
-
Apply rubbing alcohol and warm water to loosen the resin.
-
Gently twist and tap the downstem with a rubber tool.
-
Use ice water to slightly shrink the glass if it’s expanded due to heat.
If your downstem is beyond saving, it’s time for an upgrade.
Small Upgrade, Big Difference
Your downstem controls airflow, diffusion, and smoothness, making it the most underrated part of your bong.
The wrong size or style can hold back your setup, while the right one transforms every hit. If your bong isn’t delivering the smooth, effortless pulls you want, the fix is simple—upgrade your downstem. It’s a small change that makes a huge difference.
Explore high-quality downstems at Thick Ass Glass and take your bong to the next level.