Fig. 10 represents a key-head bolt, with a slot for a key, which is driven into the slot or key-way after the bolt is put into its place; such bolts being used in circumstances that do not allow room for an ordinary bolt-head. In many cases a careful smith can cut the key-ways by punching, thus avoiding the drilling process. The punching is performed by thin oblong punches instead of round ones. If a key-way of considerable length is required, the bolt is placed into a half-round bottom tool, and a small hole or slit is first punched at each end of the place of the intended key-way; the middle portion is next punched out in small pieces by the same punch. By driving the punch half way through the bolt from both sides of it, instead of from one side only, the key-way is made tolerably central. If a short key-way only is desired, the punching is performed with a punch whose end fits the intended key-way.

After being punched, a steel taper drift is driven into the opening, which becomes gradually smoother and larger, till the required dimensions are attained. The angle subtended by any two sides of these drifts should not exceed one degree; for this reason the lengths of the drifts require to be three or four times the thickness of the bolt to be punched or drifted. The extremities of the drifts are curved, to avoid trouble in driving them into and out of the key-ways.

During the use of the drifts and punches, a slot-bolster is between the work and the anvil, to permit the small end of the punch or drift to project into the slot. The dimensions of the slot are greater than of the required key-way in the bolt; and the height or width of the bolster from the anvil is sufficient to prevent the point or extremity of the drift touching the anvil while being driven into the key-way.

The drift being of taper character, renders the key-way also taper. By driving the drift to an equal distance from both sides of the bolt, the key-way becomes lai'ger at the two mouths than at the centre of the bolt. Parallelism of the key-way is attained by means of a parallel filler. This filler is made of steel, and to the exact dimensions of the intended key-way. While the filler is in, the bolt is rounded by rounding-tools, which produces the required cylindrical form for the bolt, and at the same time the desired parallelism in the key-way. If the bolt becomes nearly cold while the filler remains in the key-way, it is necessary to re-heat the part, that the filler may be easily driven out by a soft iron punch or drift.