The biggest difference between the design of the chamfer gage and the countersink gage is the way in which the plunger works. In the chamfer gage, the plunger is angled at a degree greater than the angle of the chamfer. This ensures that it comes into contact only with the biggest diameter. The plunger also is made up of three fluted or grooved sections. The plunger of the chamfer gage can either be replaceable to cover a wide range of angles or you can have two separate gages, one covering 0 to 90 degrees and another covering 90 to 127 degrees. The plunger on the countersink gage is a conical shape. This shape allows the plunger to fit very closely against the surface of the bore being measured. A slight variation between the plunger and the bore is okay, but the closer to exactly match the better. A separate countersink gage will be needed for each different angled countersink hole.