How to Measure your Downstem or Diffuser when looking for a replacement for your Bong or Dab Rig.

So you passed your piece to a mate for a hit and Mr.Clumsy MOFO dropped it and broke the downstem? Or you have heard how great the RooR Diffuser is and fancy getting one for your piece but don’t know how to measure your downstem? Never fear here is our definitive guide to measuring both the joint size of your piece and the correct length of your downstem.

First things first, what size joint you sucking?

Every glass piece in the main both in the sci-glass realm and even in custom bespoke glass work operate to set sizes. These sizes are produced in their millions for scientific glassblowers to use. We just use the same glass pieces for ease of use.

So how do you tell a joint size?

The joint size is calculated by measuring across the top of your joint using a ruler that has millimeters marked on it. You then measure your joint across the top to determine what Joint size you have, it really is that simple. (Your little finger will fit to the first knuckle on a 14.5 and to the second knuckle on an 18.8 if you dont have a ruler)

Sometimes a piece will come with a reducing ground joint. This means that the inside joint most commonly would be 14.5 for your slide BUT the bong joint would be 18.8 for the downstem. You will no doubt know if you own a piece like this as the bowl will not fit directly into the bong joint.

How to make sure I buy the right downstem length?

This is even easier than you can imagine but it’s very important that we get the measure from the right place. So first things first… do you have a downstem for your piece? If so go to Step 1. If you don’t have a downstem for your piece or it is broken into a thousand pieces go to Step 2.

Step 1


Take a ruler or tape measure that has millimeters on it and measure from the top of the ground joint that fits into your piece. Don’t worry if you don’t have a metric ruler you can always use an imperial ruler then convert the inches into millimeters -1 inch = 25mm. See the diagram. You’re measuring from the top of your downstem to the tip of your downstem and that is the length you need. You can now buy a downstem that is that length. It will fit perfectly – if you are buying a roor diffuser we often recommend going .5mm smaller to allow for variations in the ends of the diffuser downstem – due to them being entirely handmade.

Step 2

My downstem is broken what should I do? First, get rid of any broken glass you don’t want to cut yourself. Then find a piece of dowel or a pencil would do it for smaller pieces. So long as it fits through the joint without touching the sides would be fine. You also need to grab a pen to make a mark on the wood.


Now using a ruler measure that distance and take 1cm off and that is the length you need to replace your downstem. Take off 1cm so your downstem fits perfectly.


We hope this tutorial fully covers everything you need to know about measuring your piece for a refit or upgrade. Our knowledgable staff are more than happy to answer questions.

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