a plurality of rods 31 which extend from one side of the tube 19 to the other and are rotatably received at each end thereof in openings in the tube 19 a plate 32 is attached to each one of the rods 31 and these plates 32 are rotatably movable as the rods 31 are rotated a lever 33 is rigidly attached to one end of each of the rods 31 and turning of the lever 33 causes a corresponding turning of the respective rod 31 and respective plate 32 a coupling bar 34 is pivotally attached to one end of each of the levers 33 as can be seen in fig6 and 7 and this coupling bar 34 has a plate 36 rigidly attached thereto the plate 36 has a groove 37 disposed therein through which is disposed a bolt like projection 38 having a wing nut 39 threadedly engaging one end thereof the projection 38 is of course fixed with respect to the tube 19 it can be seen that in fig6 the damper mechanism 17 is in the open position and allows air to pass from the atmosphere into the lower plenum chamber 18 so that the air can pass through the perforated floor 15 and then through the grain 25 and out the top opening of the bin 13 when it is desired to close the damper mechanism 17 the wing nut 39 is loosened and the coupling bar.