These pin gauge sets and libraries contain Go (Plus) pin gauges in Class ZZ tolerance and are used to confirm that a hole’s diameter meets the minimum spec size. If the Go or plus gauge fits into the bore or hole, then the hole is within the acceptable tolerance of minimal size. Class ZZ gauges are for general purpose use and come in plain uncoated steel or with a black oxide coating that alerts users when the gauge is showing signs of wear and may need to be replaced. Go (Plus) pin gauge sets consist of dozens or hundreds of pins in a portable case with the sizes of the pin gauges clearly marked. Libraries are stationary file cabinets or metal tool chests with multiple drawers containing hundreds or even up to a thousand pin gauges organized by their increasing diameters.