Countersink gage
A countersink gage consists of a plunger and a ratio indicator that measures the biggest diameter in a countersink hole. Countersink gages have a single, solid, conical plunger that matches the exact angle of the countersink hole that you are measuring. The analog and dial countersink gages provide a 1 revolution direct read thus eliminating the need to count revolutions. Additionally, each countersink gage provides both a measurement of diameter as well as a measurement of form. Countersink gages cannot be mastered against just any flat surface, but require a sharp-edge ring gage for this process. Finally, countersink gages have a very small measurement range so require multiple tools in order to make multiple differing measurements.