=12. Special Bolts.=—In Fig. 9 is shown a =toggle bolt=. This device is a recent production for fastening materials to surfaces having a hollow interior that will not admit the use of expansion or tap bolts because of its frail character, as, for instance, sheet metal, hollow fireproofing, etc. The toggle bolt shown in the figure is constructed with long, fine-pitch threads cut nearly to the head, so as to allow for securing thin materials. The =T=-shaped head _a_ is constructed either hollow, as shown in the figure, or of flat strip metal, and is riveted loosely to the end of the bolt, allowing the head to pivot and fold over the bolt, and thus permitting the head to pass through a small opening. The head is then tipped into its proper position, when the bolt is ready for securing in place the work to be fastened. The construction of the bolt is shown in Fig. 9 (_a_), while the process of affixing it is illustrated at (_b_) and (_c_). These toggle bolts are generally made with ³/₁₆-, ¼-, and ⁵/₁₆-inch bolts, from 2½ to 6 inches long, and of either iron, steel, or brass. SASH WEIGHTS =13. Cast-Iron Weights.=—The term =sash weight= is applied to a counterweight used for balancing double-hung, or sliding, sash. These weights are generally very rough, being made from either the poorest iron or waste iron. The stock sizes are usually long and cylindrical in form—from 1⅜ to 2¼ inches in diameter—have an eye cast in the upper end, as shown in Fig. 10, and weigh from 2 to 30 pounds, the weight determining the length of the sash weight. In Table V are given the weight, diameter, and length of sash weights as they are generally furnished to the trade, although it is almost impossible to give this data with any degree of accuracy, as the different manufacturers vary the diameters of the weights slightly, and this changes the length measurement. Square weights or special weights can be easily procured at small additional cost. [Illustration: FIG. 10] [Illustration: FIG. 11] =14. Lead Weights.=—The weight of lead is about 80 per cent. greater than that of cast-iron; hence, =lead sash weights= must be resorted to where the construction of the pockets is too narrow to permit the use of iron weights, or where heavy plate glass is used. They are also used in cases where the sash are very wide and low, as here a short weight must be used in order to obtain the necessary travel for the sash. Lead weights can be procured in either round or square shapes, and of any diameter or measurement to suit existing conditions, but they are generally made to special order. A wrought- or malleable-iron eye, or fastening, for applying the cord or chain is usually inserted at the top. The cost of lead weights, however, is generally five times as great as that of iron weights.