This MSA Comfo 815185 Metallic Mercury Vapor and Chlorine cartridge with P100 particulate filter is designed to provide great protection and is fully approved by NIOSH. The P100 filter is 99.97% efficient against all particulate aerosols. The Comfo 815185 cartridge has a threaded connection type and is built to fit the MSA Ultra and Comfo respirator series. These cartridges are sold in box of 3 pair.