The most common fastening devices are nails, screws, and bolts. There are many types of nailsall of which

are classified according-to their use and form. The standard nail is made of steel wire. The wire nail is round-shafted, straight, pointed, and may vary in size, weight, size and shape of head, type of point, and finish. The holding power of nails is. less than that of screws or bolts.

The COMMON WIRE nail and BOX nail (fig. 6-83, view A) are the same, except that the wire sizes are one or two numbers smaller for a given length of the box nail than they are for the common nail. The FINISHING nail (fig. 6-83, view B) is made from finer wire and has a smaller head than the common nail, Its head may be driven below the surface of the wood, which leaves only a small hole that is easily puttied. The DUPLEX nail (fig, 6-83, view C) seems to have two heads. Actually one serves as a shoulder to give maximum holding power while the other projects above the surface of the wood to make withdrawal simple. The ROOFING NAIL (fig. 6-83, view D) is round-shafted and galvanized. It has a relatively short body and comparatively large head. Like the common wire, finishing, or duplex nail, it has a diamond point.

Besides the general-purpose nails shown in figure 6-83, there are special-purpose nails. Examples include wire brads, plasterboard nails, concrete nails, and masonry nails. The wire brad has a needlepoint; the plasterboard nail has a large-diameter flathead. The concrete nail is specially hardened for driving in concrete. So is the masonry nail, although its body is usually grooved or spiraled.

Lengths of wire nails NOT more than 6 in. long are designated by the penny system, where the letter d is the symbol for a penny. Thus, a 6d nail means a sixpenny nail. The thickness of a wire nail is expressed by the number, which relates to standard wire gauge. Nail sizes (penny and length in inches), gauges, and approximate number of nails per pound are given in figure 6-83. Nails longer than 6 in. (called SPIKES) are not designated by the penny. The general size and type of nail preferable for specific applications are shown in table 6-4.

Table 6-4.-Size, Type, and Use of Nails