Forgefix TechFast Timber to Steel CSK/Wing Screws are used to join timber to steel frame buildings. The screws are fitted with breakaway wings that create a clearance hole to protect thread from engaging timber when drilling through. Breakaway wings will ream a hole, then break-off when they contact the metal surface to be drilled. The thread will then engage with metal. They have a TORX(r) compatible insert for a higher transmission of power. With improved countersinking from recessed ribs. Fire and corrosion resistant. Complies with EU Safety, Health and Environmental requirements. These Forgefix TechFast Timber to Steel CSK/Wing Screws have the following specification: Size: 5.5 x 40mm Clamping Thickness: 20mm Effective Thread Length: 19mm Pack Size: 100 Drill Tip: No.3 No.3 drill tip for self-drilling heavy gauge steel up to 5mm.