These Forgefix TechFast Hex Head Roofing Screws are designed for fixing cladding and sheet steel to heavy section steel purlins of between 6.0mm and 12.5mm. The screws have a hex head, are self-drilling and have a rubber washer which expands under pressure to form a permanent weather seal. They are zinc plated and have an 'Elementech' coating for superior corrosion resistance, which has been salt spray tested to 1,000 hours.