What instrument is used to measure shaft runout?

The instrument used to measure shaft runout is a dial indicator. This tool is specifically designed to detect small deviations in linear movement, making it ideal for measuring the perpendicularity of a rotating shaft to its bearings. When measuring shaft runout, the dial indicator is mounted in such a way that the probe makes contact with the surface of the shaft. As the shaft rotates, any variations from a true circular shape can be observed through the movement of the dial indicator's needle. The dial provides a clear and precise measurement of these variations, which is essential for ensuring proper alignment and functionality in mechanical systems.

Other instruments such as calipers and micrometers are more suited for linear measurements and determining the dimensions of parts, rather than measuring angular or rotational discrepancies. A plumb bob is typically used for ensuring vertical alignment, but it does not provide the necessary capability for measuring the runout of a rotating shaft. Thus, the use of a dial indicator is the most appropriate choice for this particular measurement task.