Roofing & Cladding Self Drilling Screws Pack of 100 Premium self drilling roofing and cladding screws. Size: 5.5 x 51mm. Washered self-driller with hex head for a 8mm socket. For fixing cladding and sheet steel to steel purlins. Zinc plated Elementech coating for superior anti-corrosion - salt spray tested to 1000 hours. The 16mm rubber washer beneath the aluminium flange expands under pressure and forms a permanent weather-seal. Designed for fixing cladding and sheet metal to light and heavy structural purlins as used when constructing industrial units.