Cartridges provide respiratory protection against gases and vapors by using sorbents to purify the inhaled air. For dust and aerosols protection add add a particulate filter. The outer casings are made from a durable, lightweight material, and color coded for quick and easy identification. The cartridges are approved for use with both half mask series 7700 and 5500 along with the 7600 series full face pieces; you only need one inventory of cartridges and filters. All cartridges are NIOSH approved, meet 42 CFR 84 requirements, when used with North® air-purifying respirators. 2 cartridges per pack. 18 packs per case. Sold by the pack.