Red, Chicago plenum, 2-1/8" deep, 4-11/16" junction boxes with air tight (8)1/2" side and (3) 1/2" & (2) 3/4" bottom knockouts are larger boxes that are installed when larger sized conductors are required in plenum spaces. They are painted red to easily distinguish them as fire alarm circuits. These boxes are great for industrial applications. Garvin Industries’ 2-1/8” deep boxes provide extra volume for wiring and devices.