Our factory is a professional manufacturer of cylinder heads, and the cylinder heads produced are blocked by water. Water plugging holes generally have H8 tolerance requirements. In the quality inspection, because the production batch is relatively large, we generally use plug gauges to check whether it is qualified. In the inspection of the cylinder head product, the pump pressure test found that the water blockage has water leakage. After the water plug is removed, the water plugging hole is qualified by the plug gauge. The inner diameter dial gauge is used to measure the roundness of the water plug hole. Leakage caused by poor sealing indicates that the plug gauge we used has been misdetected.