Forgefix TechFast Self-Drilling Stitching Hex Screws are used to join metal roofing sheet panels together. They are self-drilling up to 2.5mm. The smaller No.1 drill tip can drill through 2 sheets then engage the threads to clamp the sheets together under the head. They have an 8mm Hex head. The screws 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. These Forgefix TechFast Self-Drilling Stitching Hex Screws have the following specification: Size: 6.3 x 25mmClamping Thickness: 8mmHead Type: 8mm HexPack Size: 100 Forgefix Techfast Self-Drilling Stitching Hex Screw & Washer No.1 Tip 6.3 X 25Mm Box 100 in Silver