Spax Full thread Flat Head Screw - Patented Multi-head design featuring ribs on the underside of the head for a clean, flush or countersunk penetration into wood, sheet metal, masonry and plastics. These are coarse thread screws, made of carbon steel, available in a silver zinc or yellow zinc finish (more sizes available in silver). Thread serrations reduce the torque required to fully drive these screws. For use with either a Phillips or Square Drive bit. Self drilling/self tapping. Spax will only offer these in 1 lb retail boxes beginning in 2021 with a higher cost per screw. Sale of these larger "contractor boxes" is limited to supply on hand. Engineered in Germany....made in USA.