Domino Clamps

How to attach steel scaffolding tube to a shipping container

How to attach scaffold tube to a shipping container.

Welcome to the first part of our Bolt-Ons series, so-called because we’ll be showing you things that can ‘bolt-on’ to the Domino Clamps.

To kick things off, we’re going to show you how to attach metal tube to a Domino Clamp, which is one of the most useful and versatile starting points to help you build or attach further structures like floodlights, CCTV and signs. 

Many of the additions we’ll be discussing in the coming months will refer back to this article.

What exactly is scaffold tube?

For those not in a country where ‘tube and fitting’ scaffolding is commonly found, we mean steel tube with a 3.2mm wall and a 48mm (more accurately 48.3mm) outside diameter which in conjunction with various types of scaffolding clamp, is used to build scaffolding structures. Identically sized aluminium tube is also quite common and comes with its own set of attachments. It is generally used where keeping weight down is a factor, such as in the events industry. 

Particularly in the UK, where tube and fitting scaffolding is still the norm, this type of scaffolding tube is abundant, relatively cheap and easy to access — so that’s why we’ll be using it as our starting point. 

For those on the continent and other countries which don't use these products, you will nevertheless have something quite similar, as a lot of ‘system’ scaffolding (products like ringlock, cuplock and Layher) also use 48mm tube, so there will be some crossover here. Most event rigging companies across the world will be familiar with the aluminium equivalent. 

Illuminated lightbulb icon  NOTE:  You may notice the words ‘bolt’ and ‘screw’ being used interchangeably here. To avoid confusion; they more or less mean the same thing.  An M12 bolt and an M12 screw as far as we are concerned are the same —  it’s the application which separates them.  A screw tightens itself with a thread into an object — in this case, our Domino Clamps. — and secures in place on its own as it locks into the thread in the Domino Clamp. If it were to go all the way through and need to be tightened with a nut on the other side, then we would call it a bolt.

Method 1.1: Using a half swivel coupler with steel tube

One of the easiest ways to fix a scaffold tube to a container is by using a scaffolding half swivel coupler. These are available in both pressed steel and forged steel variations, both of which will do the job perfectly with steel tubes. 

A half swivel coupler - as the name suggests - is just one half of a swivel coupler, used for joining two pieces of scaffold tube at a variable angle (see pic below), and so they have a hole where the pivoting pin or rivet will usually go to join the two pieces together. Generally, this hole will be about 20mm diameter

A pressed half swivel coupler is held open to show the 20mmm hole in its centre.

Once the scaffold tube is clamped in place there won’t be much room above the hole, which is why you need an M12 countersunk screw with 16mm of thread (referred to as M12x16). This will neatly fit through this hole, leaving the head tucked away out of the way of the metal tube which you’ll later be clamping the coupler to. 

To do up the countersunk bolt, you’ll need an 8mm hex key/ Allen key which can be screwed directly into any one of the four M12 holes on the front face of the Domino Clamp. 

First, hold the half coupler at the angle you require, pop your countersunk bolt through the hole in the coupler, and simply tighten up with the hex key. With just one half coupler, there’s not a lot to stop your entire pole from pivoting, so you’ll probably want to be using these couplers in pairs, either vertically or horizontally on the side of the container. 

Chris holds a scaffolding pole which has been attached to the bottom corner casting of a shipping container using a combination of Domino Clamps and a scaffolding half swivel coupler.

Method 1.2: Using a half swivel coupler with aluminium tube

It's best not to use these steel half swivel couplers with aluminium tube; particularly the pressed couplers because they can easily crimp and damage the tube. 

There are loads of aluminium half-couplers out there, but we recommend using the Doughty T57000 as it has an M12 hole and a stainless steel bolt, so it is better suited for life outside. That said, Doughty does not recommend it be left outside for long periods of time as it is not designed or rated for long term exposure to the elements, only that it is better suited to this than its clamps with normal non-corrosion resistant bolts. 

With these half couplers, use a socket cap screw instead of a countersunk one. For the Doughty T57000 half coupler just mentioned, an M12x35 socket cap screw is what you need, and we will have these for sale in our shop. 

A diagram showing the three different types of half coupler and which tube and screw they should be used with.

One downside of using a half coupler to attach the metal scaffolding tube to the container is that it leaves the scaffold clamp bolt poking out, which someone could catch their clothing or body on. It also holds the scaffold pole very close to the container, meaning that if you then want to attach another scaffolding clip to the tube running up the side of the container, there isn't a lot of room between the tube and the container to get the clip in. This is why we prefer the following method...

Method 2: Using tube clamps

Tube clamps are often called ‘kee clamps’ or ‘Key clamps’ after one of their better-known manufacturers, and are a great modular construction material. In many ways, their usability and versatility were something we aspired to emulate when we created Domino Clamps.

A close up of Chris holding a 48mm vertical tube clamp (also known as a palm railing base style tube clamp), with an annotation showing that the distance between the bolt hols is approximately 100mm. 

Tube clamps come in a variety of sizes for different sized metal tubes: 17.5mm, 21.3mm, 26.9mm, 33.7mm, 42.4mm, 48.3mm and 60.3mm outside diameter. (Please note that some manufactures and retailers may quote these numbers slightly differently, give or take 0.2mm, so rest assured if you see tube clamps marked as 33.9mm, they are for the same tube as another company’s 33.7mm.)

In the future, we'll cover different sizes, types and manufacturers of tube clamps in more detail, but for now, we’ll stick to one type and one size — 48.3mm outside diameter. We’ll be using this to show you how to use one or two vertical tube clamps to attach a vertical metal pole to a shipping container, as an alternative to the half coupler solution above. 

Using tube clamps to fixing scaffold tube to a container is a lot more aesthetically pleasing than the half coupler option, as well as removing the issue of having the half coupler bolt thread poking out which someone could catch a hand or their clothing on; great for times where the public may be quite close to the installation. In addition to this, this method will also work for aluminium tube, which is why it’s our preferred method.   

A hand points to the three different sizes of tube clamps

The bolt spacing on the clamp we are using here is approximately 102mm across (4 inches) but because their holes are much larger than 12mm diameter, they will fit our Domino Clamps perfectly. All you need here is a 25mm-long M12 bolt to attach these straight to the front of our Domino, which you can do once it is already attached to the container. 

Make sure the central bolt of the Domino is nice and tight before you bolt on the tube clamp because you won’t be able to get to the Domino’s central bolt later. It doesn't particularly matter which pair of holes you use, though we tend to prefer the top pair. Do these up nice and tight with a washer, then simply drop in your steel pole and do up the grub screw on the tube clamp with an 8mm hex key. 

Vertical tube clamp being attached to a Domino Clamp


For attaching anything heavier or higher up, you may be better off using these tube clamps at both the bottom and top of the container, with the steel tube running all the way through the top fixing. This will significantly increase the strength of the fixing and allow you to use a full-length 6.1m (21’) tube, giving you a pole for attaching things up to 3.6m higher than the top of the container. 

Usually, tube clamps have a 50mm opening at the top and a cap on the bottom so that the tube can’t slip through. That was great for our last example, as the cap meant that you weren’t relying just on the grub screw to prevent the tube slipping, but this time, the top tube clamp is going to need boring through so that the tube can pass all the way through and continue down to the lower clamp. Most tube clamp manufacturers will bore through the clamp as an extra service if you ask. 

We offer sets of these pre-bored in our online shop, and available as a whole set of two vertical tube clamps, four bolts and four washers, so you can do what we’re doing here without any fuss. 

A side by side comparison of two tube clamps, one which has been drilled through and one which as not.

Illuminated lightbulb icon

 TIP: The technique we like to use here is to get the bottom clamp attached and in position, then attach the top tube clamp to the Domino using only one of the bolts. The tube clamp will hang at an angle, allowing you to push your pole through it from underneath, before straightening it up, lifting it past the lower clamp, and then lowering it back down into the lower clamp. Then, you can do up the grub screws and lastly add in the final bolt in the top clamp. 

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