SCREW - R4 MULTI-PURPOSE - #9 x 2-1/2" PRO-PAK T25 (GRK #01101) | GRK's R4 self-countersinking screw has a patented underhead with saw-blade like cutting teeth and six self-contained cutting pockets. Together they act similar to a circular saw-blade, transporting the drill dust away from the edge of the screw hole while cutting a perfectly clean hole into even the most brittle materials without cracking any surface treatment.