What tool is typically used to measure the diameter of pipes and tubing?

A caliper is the correct tool for measuring the diameter of pipes and tubing due to its design, which allows for precise measurements of external and internal dimensions. Calipers can measure the outer diameter of a pipe as well as the inner diameter, making them versatile for pipe fitting applications where understanding the size of various pipe types is essential for proper connections and fittings.

While a micrometer is another precision instrument, it is generally more suited for smaller measurements or more detailed work on metal parts rather than for the larger dimensions typically found in pipe fitting. A vernier, which is a type of caliper, could also be used, but it may not be as commonly referenced as simply "calipers" in everyday practice. A ruler, although a basic measuring tool, lacks the precision necessary for accurately measuring pipe diameters, especially as the tolerances in fitting may require more exact readings. Thus, the caliper stands out as the most appropriate choice for measuring the diameter of pipes and tubing effectively.