GRK's R4 Self Countersinking screw has 6 self-contained cutting pockets which act like a router and transport the drill dust away from the edge of the screw hole. They also widen the countersink hole only around the head shape. The screw head top closes the hole exactly, leaving no damaged fibers around the wider area of the head. The R4 head design is so effective that it will not crack even the most brittle materials.