These Forgefix TechFast Metal Roofing to Timber Screws have the following specification: Size: 6.3 x 25mm Steel Thickness: 0.5-1.2mm Head Type: 8mm Hex Pack Size: 100 Forgefix TechFast Metal Roofing Panels to Timber Hex Screws are used to join metal roofing panels to timber frame buildings. They have a specially designed compression control thread to prevent damage and denting of panels. No pre-drilling is required and the self-drilling T17 Gash Point on screws makes for a rapid installation. The nails are fire and corrosion resistant, protected by Elementech corrosion resistant coating, salt spray tested to 1000 hours. Complies with EU Safety, Health and Environmental requirements. They are supplied with 16mm EPDM rubber washers.