=86. Chain Bolts and Foot-Bolts.=—A type of rim bolt used chiefly to secure the standing leaf of double doors is shown in Fig. 111. These bolts are made in various sizes, finishes, and grades, and in both plain and ornamental design. In the figure, the =chain bolt= is shown at (_a_), while the =foot-bolt= is illustrated at (_b_). =87. Flush Bolts.=—Bolts that are intended to perform the same function as chain bolts and foot-bolts, but are sunk into the stile of the door flush with its surface or edge, are known as =flush bolts=. These bolts, which are illustrated in Figs. 112 and 113, are made in various styles, grades, and finishes, from the smaller kinds for cabinet purposes to the large, double-mortise extension bolt. A flush bolt with a knob is shown in Fig. 114, while a _heavy_, =T=-_handle extension bolt_ is shown in Fig. 115. [Illustration: FIG. 115] =88. Door Springs and Checks.=—During recent years considerable improvement has been noticeable in the construction of the devices known as =door springs= and =checks=. Formerly, the common =torsion rod= and =coil springs=, which are illustrated in Fig. 116, at (_a_) and (_b_), respectively, were the only articles of this kind available. These devices have been in extensive use for many years, and have performed the work of closing the door, but not without the unnecessary bang and slam made by the door when striking the jambs. This was overcome to some extent, however, by the introduction of the =air-check=, which depends on the use of an air cushion to resist the force of the spring. In effect, each check is a small air pump.