For interior/exterior use in wood, plastic, cement fibre board, particle board, sheet metal, wood decking and melamine, 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 treaent. This design enhances the R4's versatility by allowing the fastener to countersink into even the hardest woods. The head of the screw closes the hole off with precision leaving no damaged fibers around the head. They have a four threaded CEE Thread that enlarges the screw hole for the non-threaded portion of the fastener, allowing the wood to settle easily. It increases the screw's drawing strength and reduces the friction on the screw shank that lowers the driving torque. Additional features include: W-Cut: low torque, smoother drive; Zip-Tip: no pre-drilling, faster penetration; ESR-3201 approved for structural application; case hardened steel: for high tensile, torque and shear strength; and Climatek Coating is AC257 code approved for use in treated lumber. To be used with green T-25 1" bit (included).