A grain bin and deck assembly includes a generally cylindrical grain bin having an inclined roof and a substantially vertical cylindrical side wall the top of which is located adjacent to the bottom of the inclined roof, and a deck encircles at least a portion of the cylindrical side wall beneath the bottom of the inclined roof and the deck is positioned to permit access to vents on the roof. The deck is mounted to and supported on the exterior of the side wall and its side wall stiffeners which stiffeners are spaced from each other and extend substantially vertically over at least a portion of the height of the cylindrical side wall and adjacent the top of the cylindrical side wall. The deck is fastened to the stiffeners of the side wall by a support assembly which includes mounting plates having a width that extends across the width of the stiffeners, and the mounting plates have plural rows of holes which are arranged to overlie stiffeners of differing widths.