A smooth plug gauge is a measuring tool used to measure the dimensions inside a workpiece hole. The smooth plug gauge is made into two types: maximum limit size and minimum limit size. Its minimum limit size is called the through end at one end, and the maximum limit size is called the stop end at the other end. The commonly used plug gauge form is shown in the figure, with a cylinder at each end of the plug gauge, with the long cylinder end being the through end and the short cylinder end being the stop end. When inspecting workpieces, qualified workpieces should be able to pass through the through end but not the stop end.