these forgefix tec fix roofing screws are self drilling winged & have countersunk headsapplicationsuitable for use when fixing timber to light section steel thickness from 15mm to 40mmself-drilling screws have a drill-shaped point to cut through the substrate to eliminate the need for drilling a pilot hole they are designed for use in soft steel or other metals the phillips screw has four simple tapered slots it is designed so that a phillips tip screwdriver can turn a phillips screw with increasing torque when the torque gets to be too strong for the tip then the screwdriver tip winds itself out of the screw thus preventing over-tightening & or damage to the screw head the countersunk heads are designed to sink flush with substrates to leave a smooth surface finishtec fix phillips roofing screw timber to steel light section 55 x 60mm box 100