See Aluminum Tolerances
Aluminum Round Tube 6063-T5 Anodized offers exceptional corrosion resistance, light weight, good formability, and similar strength to 6063-T52, but half that of 6061. The anodized surface of this 6063 gives it a longer service life with minimal upkeep and maintenance, in addition to being visually attractive and non-toxic. 6063 anodized is typically used in applications where corrosion resistance and aesthetic are more important than strength, such as piping, furniture, architectural trim, and decorative applications. Color variations may occur from one piece to the next.
Tube is designed to act as structural support, whereas Pipe is designed to carry liquid/gas/material from one place to another.