When measuring external diameters, which tool is most appropriate?

The most appropriate tool for measuring external diameters is the outside micrometer. This tool is specifically designed to provide precise measurements of the diameter of various cylindrical objects. It features a calibrated scale and a thimble, allowing users to achieve accuracy to the thousandths of an inch or hundredths of a millimeter. The design of an outside micrometer allows for a secure grasp on the object being measured, thereby minimizing the risk of measurement errors that can occur with less precise tools.

While tape measures and calipers can also be used for measuring external dimensions, they do not offer the specialized precision that an outside micrometer provides. A tape measure is better suited for larger, less precise measurements, and calipers, although versatile, may not capture the fine details necessary for small diameters as effectively as an outside micrometer.

Feeler gauges, on the other hand, are designed for measuring gaps or clearances rather than diameters, making them unsuitable for this particular measurement task. Therefore, the outside micrometer stands out as the best tool for achieving accurate and reliable measurements of external diameters.