Torx Pan head self drilling screws are made of 410 stainless steel and have a sheet metal thread with a self driller cutting (TEK) point to pierce through 20 to 14 gauge metals.
Torx 6-Lobe Pan Head Self Drilling Sheet Metal Screws are used because of the unconventional and efficient drive style. The Torx 6 Lobe drive style is designed so that the driver will not slip out of the fastener recess during installation, since the driver is not inherently centered on the fastener. This creates a lesser chance of screw stripping as well as allowing for a higher torque installation. Torx Drive Screws are also known as 6 Lobe, Star Drive and Hexalobular.
Harder than 18-8 stainless but with less corrosion resistance, 410 stainless is commonly used to make roofing screws, siding screws and self tapping (or self drilling) screws, because it is a harder material than the metal being fastened in these types of applications.