Single Flute Countersinks should be used when multi-flute countersinks chatter or the hole is too small for a multi-flute countersink to enter. 60° Countersinks are used for centering. 82° Countersinks are used for countersinking flathead screws. 90° Countersinks are used for chamfering and deburring. 100° Countersinks are used to make screw and rivet holes.