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Technical Information

Standards and Specifications

General tube and pipe information and specifications.

The difference between Pipes and Tubes


Pipes are generally for carrying fluids and gasses, the internal diameter is critical for allowing us to calculate capacity, flow rates etc., therefore pipes are named corresponding to their approximate internal diameter or Nominal Bore, this is NOT necessarily the exact named/described diameter.

Regulations govern the size of a pipe’s outside dimensions to ensure it is manufactured in standard sizes for easy fitting, but because pipes vary in wall thicknesses, internal dimensions of pipes that share the same outer dimension may vary. For this reason, any measurement of that internal dimension can only be “nominal”. Nominal bore may go by different names, in the inch system, nominal bore is abbreviated as NB; in metric system it is “diameter nominal” (DN), or “Nominal pipe Size” (NPS) in North America.



Tubes are simply named corresponding to their outside diameter (OD):

  • Examples:
    • 50 NB Sch 80 Pipe has Outer Diameter (OD) as 60.3mm and 5.49mm Wall thickness (WT)
    • Nominal Bore of a 50NB Pipe is nearly equal to 50.8mm
    • whereas a
    • 50.8mm x 5mm WT Tube has an OD of 50.8mm
    • Tube has calculated inner diameter of 40.8mm


Interested to see case studies/examples of uses of steel tubes/pipes and how they can be used to save money versus other products? Please visit the American steel tube institute.


While every effort is made to ensure accuracy, no representation is made as to the accuracy of, and no acceptance or any legal responsibility is taken for any errors, omissions or mistakes.

How tubes are measured

Circular Tube

eg. 127 x 4.5 x 6
diameter (mm) x wall thickness (mm) x length (M)

Square Tube

eg. 200 x 200 x 8 x 6
width (mm) x breadth (mm) x wall thickness (mm) x length (M)

Rectangular Tube

eg. 300 x 100 x 10 x 6
width (mm) x breadth (mm) x wall thickness (mm) x length (M)

Bunton Tube

eg. 300 x 100 x 10 x 6
width (mm) x breadth (mm) x wall thickness (mm) x length (M)

How pipes are measured

Circular Pipe

eg. 200NB Shed40 x 6
or 200DN x 8.18 x 6
or 8”NPS Shed40 x 6
nominal diameter (mm) x wall thickness (mm) x length (M)

Get in touch with us

If you have any question, Please don’t hesitate to send us a message.



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Knights, Germiston,
EXT 3, 1401,
South Africa