What does an outside micrometer measure?

An outside micrometer is specifically designed to measure the outside diameter of round objects and the thickness of flat pieces with high precision. This tool uses a calibrated screw mechanism, allowing for accurate readings typically in thousandths of an inch or millimeters. When measuring round objects, the micrometer's anvils grip the object's circumference, while for flat pieces, it measures the distance between the surfaces, ensuring efficient and precise assessments for components such as rods, shafts, or sheets.

The other choices do not align with the capabilities of an outside micrometer. Measuring the internal diameter of cylinders would require an inside micrometer or a different set of tools designed for internal measurements. Likewise, measuring the length of rod components might be achieved with a caliper or ruler, while the angle of engine block surfaces demands an angle gauge or protractor. Thus, the correct function of an outside micrometer directly correlates with its ability to measure external dimensions, confirming that option C is accurate.