Air Box Refill 1-2-3Air Box Refill serves as an excellent replacement for Air Box filtration systems. It is also very easy to replace, and each piece is sold individually. For the best outcome, make sure you replace the individual filter within 18 to 24 months. In Air Box 1 2 3 refill, the number signifies the number of cartridges required. Specifications: SKU Model: DL HT4502 Brand: Air Box