In the workpiece shown in Fig. 1, the inner hole has a circular runout of sloping surface (outer circle) of 0.02 to 0.03 mm. Due to the high requirements, according to the routine inspection, even with the mandrel inserted into the inner hole of the workpiece, there are often errors. Because the matching gap itself has 0.02 to 0.03 mm, it is difficult to measure. In response to this situation, I used a method of taper mandrel plug with the inner hole of the workpiece to measure, and the result received the expected effect.