Type 17 Self drilling screws has a sharp, drill-like point that allows the screw to drill its own hole. High-low thread allows for easy drilling and secure hold. Self-drilling point eliminate the need for pre-drilling, making installation faster and easier. Unique thread design and high-low thread provide a secure hold in various materials. Convenience, for use on timber purlins. 5/16 socket to be used when fixing. 19x6mm Bonded washers included.