cast-steel track shall not exceed eight thousand (8,000) pounds per square inch, when the effect of impact is included. The lower track shall be made in segments from six (6) to eight (8) feet in length. All abutting ends of lower-track segments are to be planed smooth, are to have close contact throughout, and are to be bolted together by two bolts passing through holes in lugs cast thereon. These bolts are to be at least fifteen sixteenths (15/16) of an inch in diameter.

In no case shall the upper track be less than two and one-quarter (2 1/4) inches, or the lower track less than two and one-half (2 1/2) inches thick, measuring on the central cylindrical surface of the drum.

The lower track shall be anchored to the top of the pivot-pier with bolts not less than one (1) inch in diameter, nor less than fifteen (15) inches long, set in place with Portland-cement grouting. These bolts are to be made of soft steel, with cold-pressed threads and hexagonal nuts at top, and with split ends and wedges at the bottom. They are to be placed in pairs opposite on the inside and outside of the track, and are to be spaced not to exceed eighteen (18) inches between centres.

The top of the pier is to be levelled off with neat, Portland cement mortar, and the lower track is to be set in same. It shall be made one and one-half (1 1/2) or two (2) inches higher in the centre than at the edge, so that the water will drain toward the latter. A small gutter or depression in the top of the pier is to be made just inside of the lower track, and at the bottom of this depression drain-holes are to be put in, leading the water from the gutter down on the outside of the pier. These drain-holes are to be at least two (2) inches in diameter; and the tops are to be protected with screens, so as to prevent choking. They are to be spaced not to exceed ten (10) feet between centres.

The rollers shall be of cast steel, and are to be made solid, excepting only the centre hole and four or more radial holes that are left in the casting for the double purpose of reducing the weight and facilitating a rapid and uniform cooling, the said holes varying in size and number with the diameter of the roller.