Countersinks are used to enlarge and bevel already drilled holes Handy when trying to insert a bolt, nail or screw flush with the drilled material The amount of flutes on the countersink determines the application Single flute countersinks are ideal for chambering, deburring, and countersinking. They provide a smooth finish on a variety of materials such as aluminum, plastic and wood 3 Flute countersinks are the most commonly used countersinks. Also called center reamers they are designed for countersinking holes for centers or for enlarging existing holes 4 Flute countersinks, also called machine countersinks, can also be used for enlarging existing holes. All four flute countersinks come with a 1/2 inch shank 6 Flute Countersinks, also called chatterless countersinks, are designed to provide more metal removal than countersinks with less flutes. They are also more effective on harder materials and provide a more shatter free cut