Black Phosphate and Oil Finish for Corrosion Resistance Star Drive to prevent stripping and ease installation Blunt tapered point with multi-cutting edges and chip cavities Type F Thread Cutting Screws T40 Drive 5/16"-18 Thread Cutting screws feature a thread cutting tip which makes threads in existing or pre-drilled holes. Made from black phosphate and oil-coated C1022 steel, these T40 floorboard screws are designed to last.