SPAX #6 x 5/8in. Flat Head Unidrive Zinc Coated Screw - 50 per Box Check out our Threads!! Our patented thread technology allows the screw to be driven faster, is easier to install, and reduces splitting in wood. Let SPAX take some of the hassle out of your next project. Heat Treated Grade 5 Durability. Subjecting the screw to heat treating gives greater strength and reduces breakage. No required pre-drilling in wood. Be more efficient on the job by eliminating time consuming steps with self drilling SPAX. Unidrive is a( Phillips/Square combo) drive system for the SPAX fastener. The user has the option of either using a Phillips drive bit or a square drive bit for installation. Patented MULTIhead countersinks the screw head flush in wood. Keep a smooth surface on your project for greater design and functional qualities.