Rectangular tubes are formed from coils and then ran through a series of dies. They are welded from the inside to form their shape. Rectangular tubes are generally used for maintenance and structural purposes. Some examples of applications would be building construction, railings, and truck frames. They are measured by their outside dimensions and their wall thickness.
Rectangular Tube is commonly available in Aluminum, Stainless Steel, Hot Rolled Steel and Cold Rolled Steel. It can be purchased online and at any Metal Supermarkets location. It can be cut to your exact specifications.