An example of this important difference can be outlined when thinking of the bolts used to assemble an airplane. In this situation, a countersunk hole is used. Since the design of a countersink hole allows for a fastener head to properly bear, these will be ideal for the airplane structure. If the hole is not deep enough, the protrusion of the bolt increases air resistance dangerously. However, if the hole is too deep, the bolt is unable to hold enough material on the surface against the underlying frame of the airplane. Both of these problems become exponentially bigger when you consider that there are thousands of bolts used on any one airplane. Using a countersink gage in this case will be preferable to using a chamfer gage in order to guarantee the proper fit and measurement of the countersink hole.
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