What tool would you use when measuring small holes?

When measuring small holes, the most suitable tool is a telescoping gauge. This instrument is designed specifically for measuring the internal dimensions of holes, such as their diameter, and it can capture the exact size of a hole's interior by expanding and contracting to fit snugly within the space. After it is inserted into the hole and adjusted to capture the internal dimensions, the gauge can be transferred to a calibrated measuring tool, like a micrometer or caliper, for precise measurements.

Other tools, while useful for different measurement tasks, do not serve this function as effectively. A caliper is more appropriate for measuring external dimensions, larger distances, or surface features, while a micrometer is typically used for measuring small objects or features where high precision is necessary, but it does not directly measure the interior of a hole as efficiently as a telescoping gauge. A depth gauge, on the other hand, is primarily utilized for measuring depth, which does not apply to measuring the diameter of holes. Therefore, for the specific task of measuring small holes, the telescoping gauge is the optimal choice.