VKC243GREEN 100mm Green Gravity Grille Vent *4" Spigot* Perfect for cooker hoods, extraction systems and tumble dryers. The 100mm Diameter Gravity Grille Round Spigot is manufactured from Polypropylene. It has a male spigot for connection inside of the system 100 duct. It is supplied complete with 3 anti-backdraft shutters which will open during fan operation and close when the fan is switched off. It will prevent external airflow or wind pressure from travelling up the duct and into the property. VKC243 is manufactured in compliance with Domestic Plastic Ductwork Specification DW/154 and meets UL94HB flammability standard.