Metal Ducting Connector - Fittings to Fittings This female duct coupling is designed to join two male duct fittings such as 90 / 45 degree bends or reducers together. This item is designed for use with safe seal galvanised metal ducting but it can be used with equivalent standard metal ducting or some plastic ducting ranges. Common applications for this coupling include as part of air extract ductwork for Bathroom or Kitchen extractor fans tumble dryers or cooker hoods. It is also perfect as part of a longer duct run such as for hydroponics in-line ventilation systems air conditioning heat recovery systems or positive pressure / input ventilation systems.