MSA 815364 Advantage Chemical and Combination Cartridge, Organic Vapor, Acid Gas, P100 Filter Type (Pack of 2) Respirator cartridges feature bayonet-style design for quick mounting Cartridges lock into place with one twist Complete range compatible with all MSA Advantage facepieces PN 815140 is only the individual cartridge. PN 815140 is only sold as a two pack which is the PN 815364.