The NBC-77 SOF filter canister, in combination with a full-face mask, mouthpiece assembly, or PAPR, reliably protects air passages against a wide range of harmful and highly toxic substances including all known CBRN agents. The filters are produced with standard round threads according to STANAG 4155 (EN 148- 1)- Rd 40x1/7"". The filter components are made of hard plastic. This results in a very robust product that is extremely durable against shock and impact damage in operational use. KEY FEATURES: Compatible with standard 40mm NATO threaded respirators, which are widely available. 20-year shelf life - save money long-term by not having to replace your Mfg: Mira Safety