3M FR-M40-20 Full Facepiece Respirator Gas Mask US M + FR-64 Filter + Black Bag. 3M FR-M40-20 Gas Mask Series Field Protective Full Face, US, Size Medium in OD Green. USGI M40 military gas mask, also known as the 3M FR-M40 series full facepiece respirator. Was designed to protect from field concentrations of chemical and biological agents, as well as radiological fallout particles. The mask features a six-point head harness and large eyepieces for a wide field of vision. It has ambidextrous 40mm NATO filter adapter ports. The facepiece is made of olive-colored silicone rubber for a good fit and comfort. An integral drinking device permits the user to replenish fluids without removing the mask. 3M FR-64 NIOSH Respirator Filter – expired 2008 / 07. Gas Mask Carrier / Pouch / Bag in Black. See photos for condition.