Double countersunk reduces the likelihood of head shear and assists completion of countersinking Wax lubricated to enhance screw insertion time, extra driving torque and resistance to corrosion 40° deep single thread to provide a secure fixing with high pull-out resistance 25° sharp point and single lead for a fast start and improved thread acceptance All sizes up to and including 75mm are fully threaded and lengths 80mm and above all have 70mm thread length