** Use at your own risk!
It is threaded in 40mm (specifically; It uses the Rd40 x 1/7" thread (NATO Standard), making it compatible with most gas masks, particularly all current NATO gas masks. The modern production C2a1 filters are sealed in a plastic container to keep the filter components fresh and unexpired. The latest run of C2a1 gas mask filters are marked (ASZM-TEDA), C2a1. The (ASZM-TEDA) signifies that these canisters are manufactured with a new type of Impregnated Carbon which offers increased protection against Chemical agents. It still does not offer full protection against Ammonia-based weapons or Ammonia fumes. It probably offers some protection against these, but is not enough to protect the user against Ammonia-based agents or Ammonia fumes
The C2A1 DIN Threaded Canister is Intended to Reduce Exposure to Chemical and Biological Warfare Agents and is used by the United States Military.
• C2A1 Canister Protects the User From Up To 15 Nerve, Choking, Blister Agent Attacks, and Two Blood Agent Attacks.
• When used with the M40 face pieces, this Cartridge is NIOSH Approved for Protection from Sulfur Dioxide, Chlorine, Hydrogen Chloride, Chloroacetophenone (CN), O-chorobenzylidene Malonitrile (CS). It can also Filter Solid and Aerosol Liquid Particulates (Oil and Non-Oil Based) and Adsorb a Wide Range of Chemical and Warfare Agents Including Nerve Agents - Tabun (GA), Sarin (GB), Soman (GD), VX; Mustard Agents - H, HD, L; Tear Agents - CN, CS, OC; Blood agents - Hydrogen Cyanide (AC), Cyanogen Chloride (CK), Arsine (SA); Choking Agents - Chlorine, Phosgene, Chloropicrin (PS), and Diphenylchloroarsine (DA).
C2a1 filters can be dated using the lot number. The first number pair with letter dates the filter's date of manufacture. MMB05A035-01, for example, indicates that the filter was manufactured in February 1 of 2005 1. The number cluster has been underlined for ease of reference. These filters have an official shelf life of 10 years, but unofficially some studies place the effective lifespan at somewhere around 12 years [for the more current C2a1 canisters packaged in the plastic containers, not for the older ones packaged in the metal cans].