Daggerz 1 4" x 3 1 4" Self Drilling Plywood to Metal Screw with Wings, Star Flat Head ACQ Dagger Ultra Guard Coating, Qty. 900 Joist Hanger Nails Box thread design – Smooth driving Box thread design – Smooth driving with reliable holding strength Select a screw length and diameter that allows full panel clearance and full penetration into the steel substrate The wings on the screw point are designed to ream a larger hole in the wood and break off when they hit the metal so the wood can be drawn tight to the steel The proprietary ACQ Dagger Guard coating passes the 1000 hour salt spray test and provides excellent corrosion resistance and is approved for use in ACQ lumber