Which of the following are key components of a micrometer?

A micrometer is a precise measuring instrument used in mechanical engineering and machining, primarily to measure small distances or thicknesses with high accuracy. The key components of a micrometer include measuring faces, which are the parts that come into contact with the object being measured, as well as the lock nut, which secures the measurement in place to prevent movement, and the frame, which provides structural support to the device. The spindle is the part that moves toward and away from the anvil to take measurements.

The measuring faces make direct contact with the object, ensuring that measurements are accurate and reliable. The lock nut is crucial for holding the measurement, preventing any inadvertent adjustments once a reading has been taken. The frame's design allows for an ergonomic grip and proper alignment of the measuring faces, which is essential for precision.

In contrast, the other options include elements that either do not belong to a micrometer at all or describe components associated with different instruments, like multimeters or measuring devices with entirely different functions. By understanding the function and construction of a micrometer, one can appreciate the importance of each component in achieving accurate measurements.