Torx Oval Tapping Screws have a 90 degree countersunk angle, the convex portion of an oval head screw sits proud of the work surface.
These screws provide higher torque transfer to each surface of the six lobes. Self-Tapping screws require a pilot hole and are installed directly into sheet metal, tapping their own threads.
A2 Stainless Steel is best for low strength applications that require corrosion resistance in damp environments.