Understanding Tube and Pipe Size Standards: A Guide to Metric and Imperial Measurements

Navigating the world of tube and pipe sizes can be overwhelming, especially when dealing with both metric and imperial measurements. If you've ever come across terms like NPS, NB, OD, or DN and wondered what they mean, you're not alone! 

In this guide, we'll break down the basics of tube and pipe sizing, clarify key terminology, and introduce you to the various tube clamps we offer to fit them.

The Difference Between Pipes and Tubes

• Pipes: Designed to carry fluids and gases, pipes are measured by their internal diameter (ID).

• Tubes: Used primarily for structural purposes, tubes are measured by their outside diameter (OD).

Key Terminology

• Nominal Pipe Size (NPS): A U.S. standard that provides an approximate internal dimension of the pipe. The actual internal diameter varies depending on the pipe's wall thickness (Schedule), while the outside dimension remains the same.

• Nominal Bore (NB): Equivalent to Nominal Pipe Size (NPS).

• Diameter Nominal (DN): The metric equivalent of NPS.

• OD (Outside Diameter): The external measurement of a tube or pipe.

• ID (Internal Diameter): The internal measurement of a pipe.

• Schedule: A U.S. standard indicating wall thickness. As Schedule increases, the internal diameter decreases while the outside diameter remains constant.

How We Define Tube Sizes at Domino Clamps

At Domino Clamps, we use tubes as structural elements, so we refer to them by their outside diameter (OD) in millimetres. For imperial equivalents, we use the NPS, NB, or DN measurement, which refers to the approximate internal dimension.

Clamps Compatible with Domino Clamps

We offer two main styles of clamps for tube and pipe:

1. Interclamp Range: Cast iron "key clamp" style tube clamps available for 34mm, 42mm, and 48mm OD pipes and tubes, in various orientations.
2. Unistrut Range: "Saddle clamp" style pipe clamps, available in sizes ranging from 21mm to 114mm OD, designed for vertical or horizontal installation.

For more information on what clamps are available in which size and for which orientations, refer to our Ultimate guide to attaching metal tube to a shipping container 

Understanding Tube Clamp Sizing

Sometimes, you may notice discrepancies in tube clamp size labelling. For instance, a tube clamp labeled as 48mm may actually be 48.3mm. This rounding is common across manufacturers. However, be mindful that 48mm and 50mm tubes are not interchangeable—a 50mm OD tube will not fit in our Interclamp range of 48mm tube clamps, but it will fit in size E Unistrut pipe clamps.

 

Choosing the Right Clamp for Your Tube or Pipe

Interclamp Tube Clamps

Interclamp tube clamps are designed to fit steel tubing that meets BS EN 10255 (ISO 65) standards, in medium to heavy gauge, or equivalent tubing in other metals like aluminum. Tubes must have a wall thickness of at least 3.2mm for compatibility.

Because these clamps rely on a snug fit, 48mm clamps are unlikely to fit 50mm ERW steel tubes, as they are slightly too large and often have thinner walls. We recommend using standard scaffold tubes in the UK or Schedule 40 pipes in the USA.

Unistrut Pipe Clamps

Unistrut pipe clamps are more adaptable to slight variations in outside diameter. For example, the 1½” NB clamp can accommodate tubes with a 50mm OD. These clamps do not rely on grub screws, making them ideal for pipes with a wall thickness under 3.2mm or made from weaker materials like Acrylic or PVC.

What Can I Attach to a Shipping Container using Domino Clamps and Pipe or Tube?

You can use pipe or tube to securely attach various structures and accessories to shipping containers using Domino Clamps. 

Here are some examples:

• Structural Attachments – Build canopies, shelters, scaffold towers, or frames for modular structures.

• Signage & Lighting – Mount signs, banners, floodlights, or festoon lighting.

• Security & Safety – Add handrails, ladders, or access platforms to improve safety and accessibility.

 

• Utilities & Services – Support cable trays, pipework, or rainwater collection systems.

For more information on tube and pipe sizes, or to explore our full range of pipe and tube clamps, visit our shop today!

More tips & guides for your project:

For more information on attaching pipe and tube to a shipping container, check out our playlist on YouTube.

If you are attaching tube along the length of a 20’ or 40’ shipping container, take a look at our roof brackets to prevent sagging or bowing. 

Planning to add multiple accessories to your shipping container? Check out our Utility pole and range of accessories.