Nylon Screw In Plastic Spiral Expansion Anchors No Pre Drill Self Tapping Insulation Fixing Plugs for Hollow Wall Product Description The No Pre-Drill Self-Tapping Nylon Screw-In Plastic Spiral Expansion Anchor is designed for hollow brick, hollow block, cavity walls, and fiber cement board substrates where pre-drilling is either inconvenient or risks damaging the thin web material of hollow units. The anchor features an enhanced self-tapping tip and aggressive spiral thread