This flue spigot is used on oil and solid fuel Aga range cookers to provide a solid exit for the 4 inch flue pipe to sit on. It sits into the flue box then twist to lock. Seal in place with a 1 inch sausage of fire cement around it. Spigot size is about 3.5 inch wide and is made of cast iron. This can't be used on Rayburn range cookes as it is too small. Rayburn range cookers need a spigot of at least 5 or 6 inch.