3M PT4TMB ~ Fire Barrier Pass Through Triple Mounting Brackets Pair 4 in Square 7000059408 SS 5 reading diopter to help TA 5 reading diopter to help workers who have difficulty reading small print or who are engaged in small detail work The 3M Exhalation Valve Cover 7918 is designed for use with the 3M Full Facepiece Reusable Respirator 7800S Series which help protect against a variety of gases the 4 inch x 12 inch 3M Fire Barrier Pass Through Triple Mounting Brackets PT4TMB provide additional support to the device when installing three devices stacked (vertically or horizontally) together in a 1 x 3 array Used in conjunction with three 4 inch square 3M Fire Barrier Pass Through Devices