Shoemaker AFP-4X12 4"x12" Aluminum Floor Perimeter Diffuser NOTE: Fits a 4" X 12" hole (see below for overall dimensions) Reinforced with pressure lock honeycomb construction to withstand heavy foot traffic All extruded aluminum construction; 1/8" bars spaced on 1/2" centers, 0 deflection Recessed screwdriver operated opposed blade damper to control air volume for positive balance Positive volume set screw; Blades run parallel to longest dimension