The Stainless Steel Secondary Combustion™ Attachments for the Urban Fire™ Collection come in three sets that fit The Farrier™ , The Anvil™ , and The Vulcan™ fire pits. These attachments cover the air slots. The air pulled into the intake gets super-heated inside the attachment. When it is expelled through the holes at the top of the attachment, providing the top of the flames with a fresh air source, the smoke is reignited, thinning it out. This creates a cleaner atmosphere around your fire. They also protect those slots from leaking or getting clogged by ashes. The attachments also help minimize bowing of the steel as it expands and contracts with the heat. Fire Pit is sold separately.