Getting the right tool begins with correctly describing your material.
Many products have a name that for convenience only approximates the material's size.
These are sometimes referred to as nominal dimensions. Differences and difficulties in correctly describing a tube and pipe are common in the metalworking industry. Pipe is a commonly used material in the ornamental iron industry. Pipe is typically manufactured to looser tolerances and less expensive to purchase. The exact wall thickness of any one schedule changes with the pipe size.