What method is used to inspect the smoothness of deburred holes?

The method of using forefinger and thumb to inspect the smoothness of deburred holes is particularly effective because it involves tactile feedback. This technique relies on the mechanic's ability to feel any irregularities or roughness in the edges of the hole. By running a fingertip around the deburred hole, the inspector can detect any imperfections that may not be visible to the naked eye, ensuring that the edges are smooth and safe for further assembly or operation.

While visual inspection can help identify some surface defects, it may not be as effective in assessing the smoothness of a hole since it doesn't provide tactile information. Pressure testing is typically used for evaluating leaks and structural integrity, not for surface smoothness. Ultrasonic testing is another sophisticated method for detecting subsurface defects, but it is not suited for assessing the smoothness of edges. Therefore, the tactile method of using the forefinger and thumb provides a direct and immediate way to ensure the quality of deburred holes.