RObust, Hamelin double flap 4" Ratblocker with tethering kit fits securely inside the drain. Features one-way flap construction, enabling rodents to escape but not re-enter. Constructed from 2mm thick stainless steel (grade 304-2B). Galvanised Steel Construction For use Against Rats Suitable Pipe Diameter: 100mm Suitable for Plastic, Clay, Concrete & Cast Iron Pipes Suitable for Commercial Use Twin Serrated Flaps Weather-Resistant Double Flaps For Additional Protection Signature Hinge System Galvanised Steel Construction For use Against Rats Suitable Pipe Diameter: 100mm Suitable for Plastic, Clay, Concrete & Cast Iron Pipes Suitable for Commercial Use Twin Serrated Flaps Weather-Resistant Double Flaps For Additional Protection Signature Hinge System