Q1: What’s the Real Difference Between 18mm and 14mm?
The numbers refer to the inner diameter of the female joint (the hole where the bowl or downstem fits).
- 14mm – inner diameter ≈ 14.5 mm. This is the most common size, used in about 70% of all bongs and rigs.
- 18mm – inner diameter ≈ 18.8 mm. It’s larger and allows significantly more airflow.
✔ Standard for most pieces
✔ Widest accessory selection
✔ More volume per draw
✔ Better for multi‑perc systems
The practical difference is airflow volume. A larger joint lets more smoke pass through with less resistance – which becomes critical when you add a glycerin coil or multiple percolators.
Q2: Why Do Glycerin Bongs Especially Need 18mm?
Glycerin bongs are not regular bongs. They contain a sealed glycerin coil that can be frozen. This coil adds inherent airflow resistance – the smoke has to travel through a narrow, chilled path. If you pair that with a 14mm joint, the combined restriction can make draws feel labored and “chuggy.”
18mm compensates for that resistance. The larger opening restores the airflow balance, ensuring a smooth, effortless draw even when the coil is fully frozen. Additionally, if you stack multiple percolators (which many Phoenix Star modular bongs allow), the 18mm foundation keeps drag comfortable.
Q3: Is 18mm Harder to Find Accessories For?
While 14mm does have a broader selection overall, the essential 18mm accessories – bowls, bangers, downstems, ash catchers – are widely available from specialty glass brands. Phoenix Star offers a full range of 18mm parts specifically designed for our glycerin bongs, so you don’t have to hunt around.
If you already own a collection of 14mm bowls, you can still use them with an 18mm bong using a 14mm→18mm glass reducer. However, for the best performance, we recommend sticking with native 18mm accessories to maintain full airflow.
Q4: Can I Use a 14mm Bowl on an 18mm Bong?
No – a 14mm bowl will simply fall right through a bare 18mm joint. The outer diameter of a 14mm bowl is about 14.5mm, which is smaller than the 18.8mm opening.
To use a 14mm bowl, you need a 14mm to18mm adapter. This small glass piece fits into the 18mm female joint and provides a 14mm female opening for your bowl. It’s an inexpensive solution, but keep in mind that the airflow will be slightly more restricted than a native 18mm setup.
The Bottom Line – 18mm Is a Performance Standard
The 18mm joint on Phoenix Star glycerin bongs isn’t a marketing decision – it’s an engineering choice based on real-world performance requirements. It ensures that the added resistance of the glycerin coil doesn’t ruin your draw, and it gives you the headroom to expand your setup with additional percs and accessories. For the best glycerin cooling experience, 18mm is the way to go.