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.The TFHH5551 TechFast Hex Head Roofing Screws have the following specifications: Size: 5.5 x 51mm.Pack quantity: 100.