Products Main / HVAC / Reducers Reducers Description Decreases ducting diameter. Crimped on smaller end. 4-3BTR 4″ to 3″ 5-4BTR 5″ to 4″ 6-4BTR 6″ to 4″ 7-4BTR 7″ to 4″ 8-7BTR 8″ to 7″