As pictured, I know literally nothing about it otherwise.
Gas Mask Filter - 40mm Nato, Black Metal, New & Sealed
GAS MASK FILTER FP-5 POLISH ARMY 40 MM STANDARD NATO-NEW.
Genuine Gas Mask Filter / Canister Adaptor From 40mm Thread to 60mm - NEW
NATO GAS MASK FILTER ADAPTORS 40mm to 3M / 40mm blanking plug/ 60mm-40mm / Scott
Genuine British Army Gas Mask Filter Adapter 40mm TO 60mm Thread Adapter
FM12 gas mask filter screw in speech emitter plug
