=72. Transom Chains.=—In Fig. 90 are illustrated several types of =transom chains=. The chains shown at (_a_) and (_b_) are suitable for sashes weighing not more than 25 pounds, while that at (_c_) is sufficiently strong for sashes weighing over 25 pounds. These chains are fastened to cleats furnished with countersunk screw holes for securing readily to the frame and sash. When the sash is hinged at the bottom, these chains are used to limit the opening of the sash. They are sometimes employed as an additional guard, to prevent the sash from falling in case the sash lifter becomes broken. The ordinary lengths of sash chains range from 8 to 24 inches, the latter length being sufficient for the opening of the largest sash. [Illustration: FIG. 90] =73. Casement Trim.=—The term _casement_ applies properly to any hinged sash. It is, however, usually limited to windows that have a sill set some distance above the floor. Where the casement sash extends to the floor, the term _French window_ is generally applied, although frequently the terms are confused. In designing casement windows, the details of the hardware should be such that the casements can be made weather-tight; and in laying out the full-sized details for the mill work for a casement sash and frame, the available hardware should be studied, so that the woodwork may be arranged to conform to it. =74. Casement Bolts and Fasts.=—Casement sash may be provided with any good form of top and bottom bolts or hinged sash fasteners, but these should be supplemented by a good latch or cupboard catch at the center. Special =turnbuckles=, or =casement fasts=, constructed as shown in Fig. 91, are on the market. All of the catches shown will securely fasten the sash, but the types shown at (_a_) and (_d_), Fig. 91, will draw the sash tightly against the frame when the buckle, or fast, is drawn in place. In countries where casement sash are in general use, the necessary fastenings, including the top and bottom bolts, are embodied in one structure, as described in the following article. [Illustration: FIG. 91] =75. Cremorne Bolts.=—In the best work, the =Cremorne bolt= is used for casement windows. This device consists of a vertical rod divided at or about the middle of its length, thus making two pieces, and is operated by a knob, or handle, at that point. Types of ornamental Cremorne bolts are illustrated in Fig. 92. As shown, the upper and lower ends of the rods, or bolts, slide vertically and in opposite directions, being operated by the turning of the knob, or handle. These bolts are furnished with suitable strikes, either of the plate or the box form, which are attached to the window at the top or the bottom. Since the ends of the bolts are beveled, they press the two sashes tightly together and against the sash frame when they are thrown in. A single movement of the knob, or lever handle, is sufficient to release both bolts. [Illustration: FIG. 92]