Current Issue C2A1 filter.

 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.

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 [B] of 2005 [05]. 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].

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