Tube or pipe, how can you tell the difference? While similar in shape and form for round pipe and tube, there is one surefire way to tell tube and pipe apart—from the inside. The key difference comes down to their applications: pipe was initially designed to transport liquids, gases, and solids but has found its way into many load-bearing and structural applications, while tube can be used for a variety of structural applications, among others. Most tube is rolled and welded and comes in round, rectangular, and square shapes. It is measured based on the outside diameter (OD) and the inside diameter (ID) or the wall. Pipe is made slightly different and can be welded or seamless. It is tested for the amount of pressure it can withstand before bursting. This is where the term ‘schedule’ comes into play, which relates to the thickness of the wall on the pipe. Pipe is usually ordered in nominal size (OD) and to “schedule” (wall thickness). A higher schedule number indicates a thicker wall. There are some instances, however, in which different sized pipes have the same schedule number but the actual wall thicknesses differ. Talk with your rep to learn more about the differences.