A Plain Plug Gauge is a precision tool used to inspect the internal dimensions of holes or bores in mechanical components. It consists of cylindrical plugs, typically made from hardened steel, with two ends: the “Go” end, which should fit into the hole if it meets the minimum acceptable size, and the “No-Go” end, which should not fit if the hole exceeds the maximum tolerance. Plain plug gauges are vital in ensuring accurate sizing and maintaining quality control in industries such as automotive, aerospace, and manufacturing. They are simple, reliable, and help in verifying dimensional accuracy, preventing defects in assembled products.