BOLT. A spevially constrneted metallic pin for fastening together temporarily or perma nently parts of struetures or machines. Bolts for doors, windows, chests. drawers. etc.. are em ployed to fasten temporarily the objects to which they are applied, and are thrown into and out of use by keys or by means of the hand. Bolts for permanent fastenings are of various kinds, and are given various names, according to their form or the use to which they are put; thus we have round, square, hook, and eye belts as examples of bolts named according to their form, and we have foundation, rail, tire, shackle, and other bolts named from the use to they are put. The most common form of bolt is that having a head at one end and a serew-thread at the other. The threaded end is sometimes screwed into the last of two or more parts, but more generally it projects through, and a suitably fitting nut is screwed on to the projecting end. This form of bolt is made by passing heated rods of iron into a machine which automatically cults off tit proper length for a single bolt, and forges £1 head 011 one end by pressure; and the blanks thus formed are then threaded in other machines, time heated rods are fed continuously, and the bolts are forged and threaded with astonishing rapidity. Bolts of complicated shape and bolts
of larger size for special purposes are forged by ordinary blacksmith-work.
Metal bolts used on board ship are called through bolts if they extend completely through a part of the structure, and Wont' bolts if only extending part way through. Bolts having a hole in the projecting end are called cyc-boils; ring-bolts have it ring through the eye. Lewis bolts consist of an eye with a tapered lug on one side which fits in a socket in the deck, where it is firmly held by a wedge or key inserted be hind it ; these bolts are used in the decks where an eye-bolt is needed, but where it is undesirable to have any projection extending permanently above the surface,