The substitution of screws for nails in building operations is a marked feature of modern work. All kinds of trimming hardware are put on with screws, and a great deal of panel work, inside finish, etc., is put together with them. Stop beads, the casings of plumbing fixtures, etc., should be fastened with screws, and also all kinds of store and office fixtures, and Cabinet work in general, except where the joints are glued. Screws are also largely Used in making furniture. Screws possess the advantage over nails of presenting a neater appearance, greater holding power and ease in removing without injuring the material. By making holes for the screws with a bit there is also no danger of splitting the finish. The ordinary style of screw has a gimlet point by which it can be turned into the wood without the aid of a bit. The heads are made in four styles to suit different uses, as shown in Fig. 331.

Screws are made of iron, steel, brass, copper, bronze and phosphor bronze ; the ordinary screw being of iron. Steel screws are comparatively little used on account of the cost. Brass, copper and bronze screws are used for putting on finished hardware of the same material, the heads being finished to correspond with the trimmings.

Iron screws are also finished with either a blue, bronze, lacquered or tinned surface, to match the cheaper class of trimmings. Blued screws are generally used with japanned hardware and for stop beads, and wherever a cheap round-headed screw is desired. Silver and gold-plated screws are also manufactured for use in connection with similar hardware. Iron wood screws are made in twenty different lengths, varying from ¼ inch to 6 inches, and each length of screw has from six to eighteen varieties in thickness, there being in all thirty-one different gauges, so that altogether there are about 250 different sizes of ordinary wood screws in the market.

Fig.333- - American Screw Gauge.

In ordering screws both the length and number of the gauge (diameter of the shank) should be given. Fig. 333 gives the exact section of the different gauges of American screws.

Fig. 332 shows a patent screw manufactured by the Russell & Erwin Mfg. Co. It has a diamond point and can be driven with a hammer its entire length into any hard wood, and then held by one or two turns as securely as the ordinary screw.

Besides the ordinary wood screws there are the lag screws and hand-rail screws; or joint bolts, which are much used by builders. Hand-rail screws are illustrated in Fig. 311.

Lag screws have a conical point, Fig. 334, with deep threads and a square head like the head of an ordinary bolt, and are turned by a wrench. They are made from 5/16 to 1 inch in diameter and from 1 ½ to 12 inches long. They are considerably used in framing in place of bolts.

Coach screws are similar to lag screws, except that they have a gimlet point, and are not usually made over \ inch in diameter.

Bolts. - About the only shape of bolt used by builders is the common round bolt with square heads and nuts. Bolts up to 24 inches in length and 1½ inches in diameter are generally carried in stock by the larger hardware dealers; above that size they are usually made to order. Bolts with button heads, Fig. 335, either round or square under the head, are also carried in stock up to \ inch in diameter, and are sometimes preferable to the ordinary square-head bolt. Stove bolts are sometimes used in building operations. They are made with flat and round heads, as shown in Fig. 336, and in sizes varying from \ to 7 inches in length and from 5/32 to 5/8 inch in diameter.