Combining cutting-edge ultra-low particulate air (ULPA) filtration with 40 mm standard NATO threading, these P3 certified biofilters work with your existing NBC/CBRN gas mask to provide unparalleled, long-lasting protection from airborne viral and bacterial threats. These filters are vastly superior to common half-face masks in practically every scenario. Please Note: This bundle comes with 6 filters in total. Key Features: 40 mm x 1/7" NATO filter standard (EN 148-1:1999) threading P3-certified protection (according to EN 143:2000 standards) filters out 99.9999+% of biothreats (not suitable for other CBRN threats) Lightweight (100g) construction Mfg: Mira Safety