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. Engineered in Germany....made in USA. This size is now available only in small retail packs of 75pc at 3x the price (per screw). Limited supply of these 1000pc boxes.