Fig. 4 represents this kind of key; the thickest part of it is termed the head, and the portion of the head at right angles to the small or thin part is named the shoulder; the thin part from the shoulder is the stem. Such keys are used for wheels or levers for spindles whose key-beds are parallel to the longitudinal axes of the shafts or spindles. In all cases where no objection exists to a key-head projecting beyond the wheel or lever, the head is admissible, because of its utility while driving out the key. When the stem of it is hidden by the wheel, the shoulder of the head receives the blows while driving out. The tools for unfixing keys are numerous, and will be treated in another place.

To forge a key with a head involves rather more labour than making a straight one. There are three principal modes of proceeding, which include drawing down with the fuller and hammer; also upsetting one end of the iron or steel; and doubling one end of a bar to form the head.

For proceeding by drawing down, a rod or bar of steel is required, whose diameter is equal to the thickness of the head required; consequently, large keys should not be made by drawing down unless steam-hammers can be used. Small keys should be drawn to size while attached to the bar from which they are made ; the drawing is commenced by the fuller and set-hammer. Instead of placing the work upon the bottom fuller in the anvil, as shown for forging a key without a head, the steel is placed upon the face of the anvil, and the top fuller only is used, if the key required is large enough to need much hammering; but a very small key can be drawn down by dispensing with the top fuller and placing the bottom fuller in the hole, and placing the work upon the top, and then striking on one side only, instead of rotating the bar or rod by the hand. By holding the bar or rod in one position, the head is formed upon the under side of the bar; and by turning the work upside down, and drawing down the lump, the stem is produced. A learner should make a small key in this manner by his own hand-hammer only ; and, having drawn the stem, he should cut off any unsound part at the end, and then cut off the key from the bar by the anvil-chisel; after which take out the anvil-chisel, and put in the bottom fuller, and draw down another key. When he has thus drawn and cut off a sufficient number, he can heat them again, and shape the heads. The set-hammer is useful to square the corner near the shoulders, and also to draw down the stems of very small keys, for which the drawing by the hand-hammer is not convenient, through the shortness of the stems.

But large round keys with heads require the top and bottom rounding-tools for adjusting the stems to their proper diameters. A double gap-gauge is also required, if a number of keys are required to be of similar diameters. This gauge is shown in Fig. 57 ; but this is not necessary for a few only. Instead of the gauge, two pairs of callipers are used, which may be opened or closed to any required width. Callipers are made of all sizes to suit the ordinary work. One pair of them is shown by Fig. 57. A pair of these callipers is adjusted to the required diameter of the small end of the forging, and another pair is adjusted to the required diameter of the large end, the callipers being riveted together sufficiently tight to prevent shifting of the two legs with relation to each other, while in fair use, but not tight enough to prevent them opening with the application of about twenty pounds of muscular force. The method of adjusting callipers is by closing the two legs by the two hands of the operator until the distance between the legs is about a sixteenth of an inch greater than the distance required ; this sixteenth of space is then traversed by gently striking the edge of one leg against a soft piece of iron until the opening is of the distance required. Adjusting callipers by other machinery will be treated in another portion of this work.

If the work in progress is more than eight or ten inches in length, a straight-edge of iron or steel is required, to ascertain if the work is too much bent.

Large keys need a little management and attention, if being made of steel, to prevent overheating; it is also necessary to consider the proper amount of bar to be drawn down, to avoid waste by cutting off a large piece of the key after being drawn to the required diameter. Two important considerations belong to this subject, which are, the unnecessary consumption of time in drawing down more of the bar than is required, and the shape of the piece that is cut off, which is often in such a condition as to be only fit for the scrap-heap.

Previous to driving in the fuller at the commencement of the drawing down of the stem, it is necessary to determine the distance from the extremity of the bar or rod at which the shoulder of the key is to be formed, and the stem of the key to begin. The author's plan of determining this distance consists in comparing the amount of area of the key-stem required, with the amount of area of the rod of steel from which the key is to be forged. And in the process he uses this rule:-

As the mean sectional area of that portion of the bar to be reduced is to the mean sectional area of the key-stem required, so is the length of the key-stem required to the length of that portion of the bar which is to be reduced.

To apply this rule to the forging of a round key with head, such as we are now considering, it is only necessary to know distinctly the dimensions of the key-stem required, and the dimensions of the rod or bar from which the key is to be made. Both these things being determined, we will consider it stated that the key shall be made from a rod of steel whose diameter is three inches, and that the key-stem shall be eleven inches in length, and the shape of it conical, the largest diameter near the head to be two and one-eighth inches, and the diameter at the small end one and seven-eighths inches. The mean sectional diameter is therefore to be two inches. And the mean sectional area of the stem required is, consequently, three, and one hundred and forty-one thousandths of square inches. The diameter of the rod being three inches, its sectional area is seven, and sixty-eight thousandths of square inches. On paper the complete proposition is, therefore, thus indicated:-