The flame retention head surrounds the nozzle on the INOV8 waste oil burner, designed to mix the air and fuel. This stainless steel piece is very durable and can be cleaned for longevity. The fins should be symmetrical and clear of debris. When the fins get bent or charred it's time to replace it. There are two sizes of flame retention heads that fit the two sizes of waste oil burners: S200 and S700.