These are indicated by Fig. 12. Small bolts of this character are termed studs, when one end of the bolt is to be permanently fixed by being screwed tight into a hole, instead of a separate nut being used. When a nut is required for each end, the bolt is named a nut-head bolt. These are made use of when it is necessary to put the bolt into its place without disarrangement of machinery. Such bolts are also frequently used as holdfast bolts for framing, also for securing or holding down cylinders and condensers. Small studs or bolts of this kind are sometimes forged to a diameter suitable for screwing by dies, instead of being turned and screwed in a lathe by change-wheels. During the rounding and reducing of the bolts to the precise diameter required, gap-gauges or callipers are necessary to measure the bolts in a convenient and correct manner.

Bolts of all kinds, large and small, are injured by the iron being overheated, which makes it rotten and hard, and renders it necessary to cut off the burnt portion, if the bolt is large enough; if not, a new one should be made in place of the burnt one.

Long bolts that require the lathe process are carefully straightened. This is conveniently effected by means of a strong lathe, which is placed in the smithy for the purpose. Long bolts are also straightened in the smithy by means of a long straight-edge, which is applied to the bolt-stem to indicate the hollow or concave side of the stem. This concave side is that which is placed next to the anvil-top, and the upper side of the bolt is then driven down by applying a curved top-tool and striking with a sledge-hammer. This mode is only available with bolts not exceeding two or three inches diameter and of length convenient for the anvil, because in some cases bolts require straightening or rectifying in two or more places along the stems. If a bolt six feet in length is bent one foot from one end, the bent portion is placed upon an anvil, while the longer portion is supported by a crane, and a top-tool is applied to the convex part. The raising of the bolt-end to any required height is effected by rotating a screw which raises a. pulley, upon which is an endless chain ; the work being supported by the chain, both chain and work are raised at one time. It is necessary to adjust the work to the proper height while being straightened; if not, the hammering will produce but little good effect. The amount of straightening necessary depends upon the diameters to which the bolts are forged, and also upon their near approach to parallelism. A small bolt not exceeding one and a half inches in diameter need not be forged more than a tenth of an inch larger than the finished diameter; a bolt about two inches diameter, only an eighth larger; and for bolts four or five inches in diameter and four or five feet in length, a quarter of an inch for turning is sufficient, if the bolts are properly straightened and in tolerable shape. This straightening and shaping of an ordinary bolt is easily accomplished while hot, by the method just mentioned; other straightening processes, for work of more complicated character, will be given as we proceed.

After the bolts are made sufficiently near to straightness by a top-tool, the softening is effected by a treatment similar to that adopted for softening steel, which consists in heating the bolts to redness and burying them in coke or cinders till cold. A little care is necessary while heating the bolts to prevent them being bent by the blast. To avoid this result, the blast is gently administered and the bolt frequently rotated and moved about in the fire.