3M 2138 P3R (nuisance level organic vapour and acid gas) particulate Filters. Stand alone, lightweight particulate filters. Offers 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. Pack of 20 Filters (Not Pairs).