Self-tapping screws tap their own threads into a pre-drilled pilot hole. Self-drilling screws, on the other hand, feature a drill-bit point that eliminates the need for a pre-drilled hole by drilling, tapping, and fastening in one step.
Yes, most self-tapping screws require a pre-drilled pilot hole before installation. The diameter of the pilot hole should match the root diameter of the screw's threads to ensure a secure grip.
Self-tapping screws are commonly used to secure sheet metals, wood, plastics, and aluminum. They are excellent for securing light-gauge metals and hard materials where traditional screws might struggle.
The rubber (EPDM) washer provides a watertight seal. When tightened, the washer compresses to seal the hole against moisture and rain, preventing leaks and corrosion on metal roofing sheets.
While they can be removed and reused, doing so may degrade the threads they created in the substrate, resulting in a weaker hold. For critical structural connections, using new screws is recommended.