The MFD-31 Parallel Blade Control Damper is ideal for controlling air flows in Commercial, Institutional and Process air systems. Dampers are constructed with rollformed 16GA Galvanized steel single peice frame, rollformed 16GA Galvanized steel triple "V" groove blades, corrosion resistant zinc plated hex bearing pins, molded nylon bearings and zinc plated linkage concealled within the side frame. Dampers are undersized by 1/4" in both the width and height and are supplied with a 6" long 1/2" diameter hex-to-round control rod. Sizes are listed "Width" x "Height" with the largest single module size being 40" x 48", however, multipule modules can be assembled to form a larger overall bank size. Available options include blade edge seals & stainless steel jamb seals for low leakage operation, manual hand quadrant operators, 24 Vac & 120 Vac electric operators and Jackshafting.