Metal Duct Reducer Metal Ducting Reducers are robust, versatile and easy to fit to solid plastic ducting, Insulated or un-insulated flexible ducting and fan spigots. Both ends of the reducer are male and are designed to fit inside solid plastic and flexible ducting. Fan spigots and duct fittings will require a small piece of duct to enable a clean fit. Metal ducting reducers are manufactured from galvanised pressed or fabiricated steel. Lightweight with simple to fit connections.