The cases in which the pulleys are mounted in the cheaper grades are made of cast-iron, while in the better grades they are made of stamped metal. High-grade pulleys constructed of stamped metal are also provided; these are put together either by riveting the two faces of the pulley or by electrically welding them. The construction of a built-up steel pulley is illustrated in Fig. 67. The cases enclosing the pulleys are made of cast-iron, as illustrated in Fig. 68 (_a_), or they are constructed of stamped metal, as shown at (_b_). The ends of the facing of the case are made square, rounded, or auger-shaped, and are finished either rough, polished, or lacquered, or are faced with brass or bronze of any finish desired. The pulleys illustrated in Fig. 69 (_a_) are so constructed that the mortise in the frame may be readily formed by a special boring machine carrying three or four bits. This machine bores holes of a size to fit the several cylindrical portions of the stamped-metal case, as at _a, a_, a diagram of the mortising in the frame being illustrated at (_b_). [Illustration: FIG. 70] The better grades of pulleys may be procured with semi-steel, brass, or bronze wheels, and with plain axles or with ball or roller bearings. In the cheaper grades of sash pulleys, the axles are formed of common wire, while in the better grades they are made of either steel or gun metal ⅜ inch in diameter. In the best pulleys, the wheels are turned, to insure smoothness of motion, and are made with grooves for cord, ribbon, or chain. All steel pulleys built up as illustrated in Fig. 67 are of recent invention; they run smoothly, and are very easily applied. These pulleys are also made with ball or roller bearings, and may be obtained at a reasonable price. [Illustration: FIG. 71] There is a special type of sash pulleys that may be used for twin and triple windows, where it is necessary to form a narrow mullion between the windows. This pulley is known as the _Grant overhead sash pulley_, and is used as illustrated in Fig. 70. At (_a_) is a twin-window arrangement, showing the sash on the two sides double-hung, each sash being counterbalanced by means of one counterweight. By this means, the frame mullion between the two sashes can be made as narrow as 2 inches, which is an advantage where the maximum amount of daylight opening is desired. Frequently, in triple windows, the center sash, as well as the two side sashes, is made double-hung. In such a case, the arrangement of the overhead pulleys would be as shown in Fig. 70 (_b_). These pulleys provide a convenient means for arranging double-hung windows of this type, but sufficient room must be left in the head of the window to allow for the insertion of this pulley and the travel of the sash counterweights. The construction of this type of overhead pulley with roller bearings is shown in Fig. 71.