Fixed-body plug gages are one of the best ways to measure hole diameters. With this type of gage there is no rocking, as with an adjustable bore gage, and therefore it is fast and provides high performance for tight-tolerance holes. Because these gages are so easy to apply, they are typically used to measure a high volume of parts. Even in cases where the volume of parts is not high — if they are expensive and the tolerance is tight — a fixed-body plug may still be an economical choice for the application. There simply may be no other way of measuring the critical part tolerance required.