COUNTER SINK 3/8 X 1/8. The Type C countersink is designed for use in all woods, plastics, and non- ferrous metals. The countersink is held in place with 2 hex socket set screws fastened into the flutes of the drill. This countersink is mounted on taper point drills. This combination can be used to drill and countersink clearance through the material for screws and bolts or to drill pilot holes for other types of screws.