The track for these doors is best made of round-edge bar iron or tire steel, ⅜ in. × 3½ in., being bolted to the wall with through bolts having nut and flanged washer on the opposite side, and held from the wall by cast-iron track brackets. The hangers are of wrought iron, ⅜ in. × 3½ in., provided with roller-bearing wheels and are attached to the door with at least two bolts. The binders are of wrought metal, ⅜ in. × 3½ in., with angle flange at back end to notch in the wall and so arranged as to grip and force the door against the wall when closed. In connection with this, a wedge is placed at the end of the lower chafing strip, and, when the door is closed, engages with the stay roll so that the door will be held close to the wall on the opposite side. Two chafing strips of ¾-inch, half-oval metal are placed on back of door with 1" × ⅛" flat strips of same length in front and bolted through the door. Bumper shoes are also used to prevent the binders from mutilating or damaging the tin covering at the points that strike the binders. =90. Door Knockers.=—Although the medieval =door knockers= have been replaced by the modern door and electric bell, they are still used occasionally for decorative purposes, and, when required, they should be selected and specified with the finishing hardware. Door knockers are made in various styles, sizes, and finishes—in iron, brass, or bronze—to match the several designs expressed in hardware. The elaborateness of the designs of this somewhat ornamental piece of hardware is shown in Fig. 128. [Illustration: FIG. 128] [Illustration: FIG. 129] =91. Water-Closet Door Trim.=—The construction of water closets in public buildings has brought forth special hardware to meet the various conditions of convenience, simplicity, and hard usage. In ordinary work, the doors of water-closet compartments are secured with a hook or a barrel bolt, while in the better class of work, as in hotels and public places of this character, mortised thumb or knob bolts or, better, indicator bolts are used. =Indicator bolts=, as shown in Fig. 129, made both mortise and rim, are available for water-closet doors. In either case, the bolts are mortised into or placed on the inside of the door with the indicator case on the outside. The indicator dial has a spindle on the back, and this engages with the knob that operates the bolt. When the bolt is thrown, the indicator shows the word “Engaged,” and when turned back, the word “Open” appears. [Illustration: FIG. 130] A simple form of fastening for water-closet doors is shown in Fig. 130, which illustrates the flush, or half-mortise, knob bolt at (_a_), and the water-closet rim latch at (_b_). The rim slide bolt is also used for securing water-closet doors. All of these bolts are available for wooden partitions, and may be had for marble or slate work, when special strikes and bolts for fastening will be required.