The MFS-40 Barometric Shutter is constructed using an extruded aluminum frame and counterbalanced fabricated aluminum blades featuring Celcon pivot pins for strength and non-binding nylon bushings for smooth eration. Shutters are undersized by 1/4" in both the width and height. Sizes listed are Width x Height with the largest single module size being 24" x 24", however, multipule modules can be assembled to form a larger overall bank size.