=9. Drive Screws.=—A screw known as the =drive screw= is used mostly in the manufacture of various articles where cost is the controlling factor. These screws, shown in Fig. 6, are made somewhat on the order of the wood screw, but without the deep-cut thread and gimlet point. Screws of this type are driven into the wood with a hammer and have slotted heads so that they may be withdrawn by means of a screwdriver. The thread is so constructed that the wood may be penetrated without breaking down its fiber when the screws are driven, and is shaped so as to engage with the wood while resisting a pulling stress. These screws are made with flat, round, or oval heads, as illustrated respectively at (_a_), (_b_), and (_c_), and may be had in sizes from ½ inch to 4 inches in length. [Illustration: FIG. 6] =10. Expansion Bolts.=—The =expansion bolt= is a device that has proved extremely valuable in the building trades, as it provides a means of bolting to stone, brick, concrete, slate, or other materials of this nature. Expansion bolts are used principally in places where it is not desirable or practicable to drill through the material to which the fastenings are to be made. This type of bolt has also a great advantage over other fastenings in that it can be removed with as much ease and facility as it is applied, and also without injury either to the article fastened or the material to which it is fixed, the bolt likewise sustaining no injury. Many styles of expansion bolts are now manufactured under various patents, and these may be procured in all sizes and made of iron, steel, or brass. In Fig. 7 are shown several makes of expansion bolts. The _McCabe expansion bolt_, shown at (_a_), is constructed of a malleable, cylindrical-shaped, slotted case, or shell, _a_, the aperture of which reduces in size and engages with a bevel-shaped hexagon nut _b_. By turning the bolt, the nut is drawn toward the head and thus expands the outer case in its passage; this in turn binds against the sides of the hole in the masonry into which the bolt is inserted. The shell, as the outside case _a_ is called, can be procured in any length or diameter, and can be used with any machine bolt having a standard thread. The McCabe bolt is suitable for bolting any thickness of material, provided the proper length of bolt is employed. The _Brohard expansion bolt_ shown at (_b_), performs the same functions as the bolt illustrated at (_a_). The case, or shell, _a_, is composed of two or more parts riveted to a wrought circular plate, near the head, as at _b_. These several parts are expanded by means of the beveled nut, which approaches the head as the bolt is turned. The principal feature of the Brohard expansion bolt is that the beveled nut _c_ cannot be forced from the case on account of the lug _d_, which is attached to the nut and travels in the slot _e_ when the bolt is turned. [Illustration: FIG. 7]