The ties consist of flat wrought-iron bars, 7 inches by 1 inch of best scrap iron, with eyes of 3½ inches diameter, bored out of the solid, and pins turned and fitted closely. Each external rib is tied by four of these bars, and each internal rib by eight. The sectional area of each external tie is 28 inches, and of each internal tie 56 [square inches, giving a total area of 168 square inches. These bars were all tested to 9 tons on the square inch.