Countrsink
To enlarge the outer end of a hole for the reception of the head of a screw, bolt, etc. A tool used to turn out or countersink. Figs. 100 and 101 illustrate Happersberger's patent, flat-bottomed countersinks, which are designed for making or deepening flat-bottomed countersinks for screw heads of any kind. The screw-thread or hole will not be injured in using these tools. Fig. 102 illustrates a set of wheel countersinks made with cutters on one end and burnishers on the other. Countersinks are also made from steel in the form of drills and from emery in the form of a cone, with metal handle for revolving. The emery countersink will be found very useful for large holes and for trimming the edges of holes in enamel dials.