How to Measure a Bong Downstem Correctly

A downstem is the glass tube that connects the cone piece to the water chamber inside a bong. Smoke travels through the downstem before entering the water.

Many glass bongs use a removable downstem, making it easy to replace if it becomes damaged or broken.

Downstems are available in different:

• Joint sizes
• Lengths
• Colours
• Glass thicknesses
• Diffuser designs
• End styles

That is why simply buying a stem that looks about the same is not always enough.

When replacing a bong downstem, check two things.

Joint Size

This tells you the diameter and fitting type of the glass connection. Common Billy Mate downstems use a 19/14mm configuration. That means:

• The 19mm section fits into the bong
• The 14mm opening accepts the cone piece

We explain this in detail in our 14mm vs 19mm Bong Joint Size Guide.

Stem Length

This determines how far the downstem extends inside the bong. The length is especially important because the bottom of the stem needs to sit correctly inside the water chamber.

A stem that is too short may not reach far enough. A stem that is too long may hit the bottom or side of the bong.

Remove the downstem from the bong and place it on a flat surface. You will usually see three main sections:

• Ground glass joint
• Straight glass tube
• Diffused or open end

There are two useful length measurements.

Measurement 1: Overall Downstem Length

The overall length is measured from the very top of the downstem to the very bottom. This includes the entire glass piece.

For example, a Billy Mate stem might have an overall length of 12cm, 13cm or 16cm. This measurement is useful when comparing replacement stems, but it is not always the most important measurement.

Measurement 2: Joint-to-Bottom Length

This is the measurement to pay closest attention to. Measure from the bottom edge of the ground glass joint to the very bottom of the downstem. This tells you approximately how far the stem extends into the bong once installed.

For example, a stem might have an overall length of 12cm and a joint-to-bottom length of 9cm. That is much more useful than simply knowing the total length.

Imagine two downstems are both advertised as 12cm long. At first they appear identical. But one might have a longer ground joint section than the other. That means the amount of glass actually extending inside the bong can be different.

This is why Billy Mate product specifications may include both the overall length and the joint-to-bottom length. It makes choosing a replacement much easier.

Do not measure from the point where the stem happens to sit inside the bong. Instead, remove the stem and look at the frosted or ground glass joint. Measure from the lower end of that ground joint section down to the bottom of the stem. That gives you the joint-to-bottom measurement.

For overall length, simply measure from the absolute top to the absolute bottom.

If you still have most of the original stem, you may be able to determine the correct size. First measure the joint. Then estimate the original length using:

• The remaining glass
• The bong chamber
• The position where the stem previously sat
• The original product specifications, if available

If the stem shattered badly and the original measurements are unknown, measuring the bong itself may be safer than guessing.

If you no longer have the original downstem, carefully measure from the bong's joint toward the water chamber. You want the replacement stem to extend far enough into the chamber without touching the opposite wall or bottom.

A useful rule is to leave some clearance. The end of the stem should sit inside the water chamber rather than pressing against the glass. Do not choose the longest stem that will physically fit.

Length is not the only thing that can differ between stems. A standard open-end downstem has an opening at the bottom. A diffused downstem usually includes several small slits or holes near the end. These openings divide the airflow into smaller bubbles as it passes through the water.

Billy Mate carries a range of diffused glass downstems, including different lengths, colours and designs. When replacing one, try to match both the size and style if you want the bong to remain close to its original configuration.

Different downstems may have different diffuser designs. Some use several narrow slits. Others use holes or combinations of openings.

The main thing when replacing a stem is still fit. A beautifully made diffused stem is no use if the joint or length is wrong. Start with joint size, then length, then choose the diffuser style you prefer.

If you are unsure whether the downstem is 14mm or 19mm, measure the ground glass joint. A digital caliper is ideal because the difference between common glass joint sizes is relatively small.

Typical classifications are:

• 14mm class: approximately 14 to 14.5mm
• 19mm class: approximately 18 to 19mm

At Billy Mate, we use the simpler product terminology of 14mm and 19mm. A common Billy Mate configuration is 19/14mm.

It means the downstem uses a 19mm male section into the bong and a 14mm female opening for the cone piece. So when buying a replacement cone piece for a 19/14mm stem, you will normally be looking for a 14mm cone piece.

Imagine you remove your old stem and measure:

• Joint: 19/14mm
• Overall length: 12cm
• Joint-to-bottom: 9cm

Your replacement should be as close as possible to those specifications. Searching only for "12cm bong stem" is not specific enough. A much better description would be "19/14mm diffused glass downstem, 12cm overall, 9cm joint-to-bottom". Now you know exactly what you are looking for.

Measuring Only the Overall Length

This is probably the most common mistake. Two stems with the same overall length can sit differently inside the bong. Check the joint-to-bottom length as well.

Ignoring the Joint Size

A perfect length does not matter if the glass joint does not fit. Always check both.

Measuring While the Stem Is Still in the Bong

Take the stem out. It is much easier to identify the start and end points accurately when the downstem is sitting on a flat surface.

Guessing From a Photo

Photos can be deceptive. A 10cm stem and a 13cm stem can look almost identical online without something beside them for scale. Use the listed measurements.

Forcing a Stem That Does Not Fit

Never force a ground glass joint. If the stem does not seat naturally, stop and check the size. Glass joints are designed to fit smoothly.

The bottom of the stem should sit comfortably inside the chamber without touching the bong wall or base. You also want the diffuser or bottom opening positioned where it can remain appropriately submerged when the bong contains its normal amount of water.

If the stem touches the bottom or side of the bong, it is probably too long. If it barely enters the chamber, it may be too short.

The correct replacement is determined by three main things:

• Joint size
• Overall length
• Joint-to-bottom length

After that, you can choose between clear glass, coloured glass, diffused designs, standard designs and decorative styles. Fit comes first. Style comes second.

Billy Mate produces downstems in multiple lengths because different bong designs require different stems. You may see options such as:

• 8cm
• 10cm
• 11cm
• 12cm
• 12.5cm
• 13cm
• 14.5cm
• 16cm

Depending on the product, both overall length and joint-to-bottom length may be listed. Always compare those measurements with the stem you are replacing.

Take 30 seconds and write down:

• Joint size
• Overall length
• Joint-to-bottom length
• Diffused or standard

Once you have those four details, finding the correct replacement becomes much easier.

Billy's Tip: If your old downstem is still intact, do not throw it away until the replacement arrives. Keep it beside you when ordering and compare the measurements. A few millimetres can make the difference between a stem that sits correctly and one that does not.

Remember:

• Joint size tells you whether it connects
• Joint-to-bottom length tells you how far it enters the bong
• Overall length helps confirm you have the correct stem

Get all three right and you dramatically reduce the chance of ordering the wrong replacement.

Billy Mate offers replacement glass downstems in different lengths, colours and diffuser designs, along with matching 14mm glass cone pieces. Check the specifications of your existing bong or measure your current stem before choosing a replacement.

If you are still unsure about the difference between fittings, read our 14mm vs 19mm Bong Joint Size Guide before ordering. And if you are choosing a new bong altogether, our Bong Sizes Explained: 20cm vs 25cm vs 30cm vs 35cm guide covers height and stability, and you can browse the full range of Billy Mate glass bongs any time.