The Evolution A4 Bi-Metal Stainless Steel Hex Head Composite Panel Fastener for Light Steel, with a 16mm Bonded EPDM Washer, is designed for fastening to aluminium sheeting and panels. A4 stainless steel with an electroplated zinc coating. Twin, high thread form with an insulation thickness range of 75-135mm and recommended drill speed of 1500-2500 RPM.