3M 2138 P3R (nuisance level organic vapour and acid gas) particulate filters. Stand alone, lightweight particulate filters, Lightweight, Low breathing resistance, Bayonet fitting system ensures precise and safe locking, Versatility: can be used on all 3M 6000, 7000 and 7500 Series Half Masks and Full Face Masks 1 BOX 20 FILTERS (NOT PAIRS).