How to Measure and Buy the Right Downstem

Know what to look for, and buy right.

Downstems are an essential part of any bong or water pipe.  They function by transporting the smoke from the bowl or slide into the water chamber for a cooler and smoother hit.  Just like the bongs and water pipes they accompany, downstems come in a large variety of sizes, and styles.

Downstem Size

Various Measurements

Buying a new downstem

When buying a new downstem for your favourite piece, the most important thing to know is size, which can actually be pretty confusing if it is your first time buying a replacement.  When it comes to downstems, we can assume the ground joint is female, but there are 3 more measurements that you’ll need:

  • Length of the Downstem
  • Ground Joint Size (the bong or water pipe joint size)
  • Bowl Size

Downstem Length

A way to measure that works

Know Your Length If you don’t have your current downstem available to measure the length, you can use a pencil or any long object that fits inside the bong/water pipe to measure the inner chamber.

Pencil Method Insert the pencil into the inner chamber of the bong through the joint opening until the tip is roughly 2 cm or 0.5 inches from the glass on the other side.  Mark the pencil and then measure from the mark to the tip.  That will be your down-stem length.

Ground Joint Size

Use a dime for reference

The Ground Joint

Measure the inside diameter of your bongs ground joint. It will be either 10mm, 14mm, or close to 19mm.  If you don’t have measuring tape nearby, you can use a dime.  If the dime fits through the hole, it is 19mm.  If it does not, it’s likely 14mm as downstems do not usually come in 10mm.

It is important to be sure of the correct size when ordering a new downstem:  wider joints obviously won’t fit, and narrower joints won’t create the air-tight seal you need for optimal performance.

Bowl/ Downstem Size

Downstems have one joint for the bowl and another to connect to the bong.  Downstems come in:

  • 14mm to 14mm (14/14)
  • 18mm to 18mm (18/18)
  • 14mm to 18mm (14/18)
  • 18mm to 14mm (18/14)

The first number represents the size of the joint in your bong. The second number represents the size of the bowl.

For example, if you see a description such as 14/20 or 14>20, this means your bong has a 14mm joint, and the diffuser you’re looking at will transform that 14mm joint into a 20mm joint.  Now you can fit a bigger bowl into that bong!

If the description was 20/14 or 20>14, your bong has a 20mm joint and the diffuser will hold a 14mm bowl.

Downstem Styles

Most commonly known

Most Popular Styles

Two popular styles of downstems are the “Flush Mount” and “High Profile”.

Flush Mount Downstems

Have an opening that does not stick out much from the opening of the joint.  The length of Flush Mount Downstems are only a little longer than the length needed in the inner chamber of the bong.

High Profile Downstems

Stick out from the opening of the bong, and can sometimes add up to between 0.5 – 1.5″ inches to the length of the bong.


Now that you’re ready to purchase a replacement downstem diffuser for your bong, check out our selection of downstems here.

If there was anything we missed, please send us a note to, or find us on Facebook and shoot us a message. We would be more than happy to answer any questions.