The advantages of screws are, that they are very strong and that the work can easily be taken apart. If they loosen they can be retightened. The disadvantages are, that they are expensive, that they take time to insert, that they show very plainly, and that they do not hold well in end grain.
Bolts with nuts are useful where great strength is desired. There are three chief varieties, Fig. 230.
[Illustration: Fig. 230. a. Stove-bolt. b. Carriage-bolt. c. Machine-bolt.]
_Stove-bolts_ are cheaply made (cast) bolts having either flat or round heads with a slot for the screwdriver, like ordinary screws.
_Carriage-bolts_ are distinguished by having the part of the shank which is near the head, square.
_Machine-bolts_ have square, hexagonal, or button heads.
_Machine-screws_, Fig. 231, are similar to stove-bolts, but are accurately cut and are measured with a screw-gage. The varieties are, _a_, flat-head, _b_, round-head, _c_, fillister-head, _d_, oval-countersunk-head, all with slots for screwdriver.
_Plates_, Fig. 232, include corner-irons, straight plates and panel-irons. These are made of either iron or brass and are used in fastening legs to the floor, in stiffening joints, affixing tops, etc.
_Dowel-rods._ Dowel-rods are cylindrical rods, from 3/16" to 1" in diameter, and 36", 42", and 48" long. They are commonly made of birch or maple, but maple is more satisfactory as it shrinks less and is stronger than birch.
Dowels are used as pins for joining boards edge to edge, and as a substitute for mortise-and-tenon joints.
[Illustration: Fig. 231. Machine-screws. a. Flat-head. b. Round-head. c. Fillister-head. d. Oval-countersunk-head.]
There is, to be sure, a prejudice against dowels on the part of cabinet-makers due, possibly, to the willingness to have it appear that doweling is a device of inferior mechanics. But doweling is cheaper and quicker than tenoning, and there are many places in wood construction where it is just as satisfactory and, if properly done, just as strong. Certain parts of even the best furniture are so put together.
Shoe pegs serve well as small dowels. They are dipped in glue and driven into brad-awl holes.
[Illustration: Fig. 232. a. Corner-iron. b. Straight plate. c. Panel-iron.]