See Aluminum Tolerances
Aluminum Round Tube 2024-T3 offers an excellent strength-to-weight ratio, high fatigue resistance, and average machinability. The addition of copper to this alloy makes 2024 one of the strongest aluminum alloys, but it also is more succeptible to corrosion than most other aluminum alloys. 2024 is typically used in aerospace applications, clock parts, computer parts, hydraulic parts, bolts, valves, nuts, pistons, and gears.
Tube is designed to act as structural support, whereas Pipe is designed to carry liquid/gas/material from one place to another.