The Evolution A4 Bi-Metal Stainless Steel Self-Drilling Hex Head Tek 5 Screw, with a 16mm A4 Bonded Washer, is designed for fastening in aluminium sheeting and panels. Material grade is A4 Stainless Steel, with an electroplated zinc coating and an effective thread length of 15.0mm. Fine thread form, drilling capacity of 4.0-12.5mm and recommended drill speed of 1500-2500 RPM.