Final answer:
The tool that would be used to measure the thickness of a solid metal rod is the outside micrometer (option D).
Step-by-step explanation:
The tool that would be used to measure the thickness of a solid metal rod is the outside micrometer (option D). Outside micrometers are specifically designed to measure the external dimensions of objects, such as the thickness of a rod. They consist of a frame, an anvil, a spindle, a thimble, and a sleeve. By adjusting the position of the anvil and the spindle, the micrometer can accurately measure the thickness of the rod.
The appropriate tool to measure the thickness of a solid metal rod is the outside micrometer. An outside micrometer is a precision measuring device used to measure the outside dimensions of objects. It operates by using a calibrated screw and provides highly accurate measurements, which is particularly useful for measuring the diameter or thickness of rods and other cylindrical or round objects.