The _Steward and Romaine double-expansion bolt_ is shown at (_c_). The shell of this bolt is composed of two semicylindrical parts, as at _a, a_, that are somewhat longer in diameter than the wedge-shaped nut and the sleeve at _b_ and _c_, respectively. Each half of the shell is held in place by light rubber bands. The wedge-shaped parts are caused to approach each other by the turning of the bolt, and thereby expand the split case at both ends simultaneously. From the fact that this bolt is expanded at both ends, it is called a =double-expansion bolt=, although it may be made single-expansion by omitting the wedge-shaped sleeve at the head. [Illustration: FIG. 8] The _Star expansion bolt_, shown in Fig. 8 (_a_), performs exactly the same duty as other expansion bolts, but its construction is radically different. This bolt consists of only two parts, called _shields_. Each shield is semicircular in form and interlocks at the joints. The exterior of these shields has four rows of corrugated ridges, or star-shaped projections, that prevent the shields from turning in the hole. The interior of the shell is threaded and decreases in size toward the farther end. Thus, by inserting a lag, or coach, screw of any length, so as to engage with the thread, the shields are spread apart at the farther end while the screw is entering the aperture. The _Diamond expansion bolt_ shown at (_b_) is practically the same as the one just described, as will be observed from the figure. Expansion bolts are also made with all the parts entirely of brass or bronze, with either plain, capped, or fancy heads, or nuts, and in any finish desired. =11. Screw Anchors.=—The device known as a _screw anchor_ can be used in place of an expansion bolt for securing light materials. Several kinds of screw anchors are in the market at present. The _star anchor_, which is made in one piece of composition metal that is slotted about seven-eighths of its length, may be obtained in various diameters and lengths. The exterior has two star-like projections, to prevent the anchor from turning, while the interior is constructed of ridges projecting from the tube, with the hole reduced toward the slotted end. This internal construction permits the star anchor to be used in combination with trade wood or machine screws of any length. The screw used engages with the ridges in the interior, cutting its own thread and expanding the anchor in its passage. These composition anchors are very cheap, the price ranging from 1 to 3 cents, according to the size. They are made in different lengths, from ½ inch to 1½ inches, and for Nos. 6, 10, 14, and 18 wood screws. [Illustration: FIG. 9]