C3 Canadian Forces Gas Mask, size - medium made by Baron in 1986 The Canadian military C3 gas mask was Canada's updated version of the British Light Anti-Gas Respirator. Early versions of the Canadian C3 used a 60mm threaded filter canister which was mounted on the cheek of the face piece. The C3 remained in service for several years and was later updated with a filter inlet coupler that allowed 40mm threaded canisters to be used to conform with NATO standards. Plastic adapter included.