Aluminum alloy; qq-a-250/11, alloy 6061, t6; 3.000 in. Od; 0.500 in. Thk o/a; 1.406 in. W o/a with u-shaped groove 0.218 in. W by 0.109 in. Dp; located on outer periphery with 3 mtg holes, 0.187 in. Id; equally spaced on 2.187 in. Bolt circle dia; holes countersunk on one side to a 0.438 in. Dia