Callipers are made of sheet steel and of small bar steel. To make an outside calliper of a short piece of bar steel, the two legs are forged together in one piece, the two thighs or joint portions being in the middle. Two legs being thus made are shown by Fig. 531, the legs being only partly bent to the curve desired. In order to effect an easy bending, the work is bent edgeways while on the anvil-beak, previous to the legs being thinned to the intended thickness; after being partly thinned, a small amount of curving is given, and after a further thinning the work is curved a little more, the final thinning being done after the legs are curved to the intended shape. The work is next cut into two, and the joint portions trimmed to a circular form.

Outside calliper-legs are also made singly, each leg being made at one end of a thin bar, and curved while still attached to the bar; a leg being thus made is shown by Fig. 534. In this Figure the end lump is shown ; this unreduced lump is always thicker than the adjoining portion while the work is being thinned, in order to avoid cracks being made during the reducing, whether two legs are being forged solid together, or whether only one leg is being made at an end of a bar. The method of making each leg singly, or a pair of legs together, at one end of a bar, is always preferable if the bar can be obtained, because the long part of the bar is a much better handle for the work than a tongs, however good the tongs may be.

Calliper-legs that are made of sheet steel are cut from the sheet or plate while red hot, after the shapes of the intended legs are marked, and a hand-chisel driven in at the marks, while the metal is cold. A plate thus marked is shown by Fig 532 ; such a piece is held by the smith on an anvil with an iron fender-plate between the work and the anvil, and in this situation the legs are cut out with a rod-chisel which is struck by a hammerman. The making of inside calliper-legs is effected by the same means as for outside ones, either thin bars or sheet steel being employed, according to the arrangements of the maker. Those who make large quantities of callipers should always make the legs of sheet metal, and provide punches and dies that are the shapes of the intended legs, so that each leg can be cut out at one stroke or effort of the punching-machine.

The circular washers with which the legs are riveted together are also of steel, and should be forged separately of a thin bar. The bar is heated to redness at one end, and a few holes made with a round punch, the holes being at a proper distance apart for each washer. In order to allow each hole to be afterwards enlarged by broaching, the hole is punched smaller than the finished diameter, and after punching, each washer is cut off, and the corners also are cut off, each one being finally rounded with top and bottom tools. To make such washers in large numbers, each should be cutout and punched at one blow with a machine while the metal is red hot, similar to the mode for punching the legs.

The smoothing of the broad sides of the legs consists in first grinding them on a grindstone, and next filing each one separately while held with a thumb-vice on a piece of wood or plate iron which is gripped in a bench-vice. A leg in such a situation is shown by Fig. 535 ; it is not necessary to finish the broad sides previous to filing the edges; it is sufficient to grind or file off the rough portions, so that a pair of legs can have a hole drilled in each, and be fixed together in a temporary manner, in order to file the edges to the desired form. Two legs thus fixed are shown by Fig. 533, and are held by means of a rivet which is about an eighth of an inch longer than the thickness of both legs together; this temporary rivet is very slightly hammered - only sufficient to hold the work together, and while fixed, the desired shape for both legs is easily obtained with filing. Both outside calliper-legs and inside ones can be thus held, and the entire edges roughly filed to shape, except about half an inch at the small end of every leg which is intended for an outside caliper ; this short portion is allowed to remain thick, to be made into a broad end, if such an end is required. A pair of these broad ends are shown by Fig. 541, and are useful for callipers that are to measure screws, thin edges, and pointed extremities. Broad calliper-ends are made by heating the end to redness, and spreading it out with a small hammer. If the leg is a small one of only three or four inches in length, it is heated in a gas-flame and hammered on a small anvil near a vice ; but large legs require heating in a forge fire, and spreading while on an anvil-beak. Another class of calliper-ends are shown by Fig. 542, which are useful for measuring the bottoms of narrow grooves, such as screw-grooves. Ends of this shape are formed with mere filing, without any spreading being required. Fig. 543 indicates a pair of pointed ends; such ends are only made to small callipers, and are shaped and smoothly polished on an oilstone after the callipers are riveted together and finished. The shapes for ends of inside callipers are shown by Figs. 544 and 545 ; those denoted by Fig. 544 are for ordinary measurement of holes and openings of various sizes and shapes, and the pointed ends indicated by Fig. 545 are useful for measuring inside screws.

After the broad sides are filed, the joint holes drilled, and the edges filed, the two washers are turned, and the thighs are prepared for a final riveting together. This preparation consists in properly broaching the holes and smoothly polishing the broad sides of the thighs, also the two sides of the washers which are to be in contact. All these six surfaces should be as smooth and as nearly plane as possible, by which means chips, file-dust, and other substances will be kept out from the joint while the tool is in use. The broaching consists in using a slightly taper half-round, or fluted broach; this is put through all the four pieces, including the two washers and the two thighs, and while the broach is in a few turns round are given while the four pieces are held in a vice, or held over a hole, and clamped with two plates. The holes in the washers are coned with a cone-driller of proper shape, to produce a deep cone instead of a shallow one, and after all the burs made upon the edges of the holes with filing and broaching are rubbed off" with smooth emery-cloth, the work is ready for riveting together with a steel rivet; this rivet is smoothly polished to provide a good bearing surface for the joint, and each end is allowed to project sufficient to be filed to a convex form, resembling that of the rivet in Fig. 546. A rivet having such extremities is easily riveted at a future time when necessary, but a flat end whicli is level with a flat washer cannot be riveted without indenting the rivet and requiring the entire side of the washer to be filed. When a rivet is hammered too much at any time, and the joint thereby made too tight, it is loosened by heating it in a gas-flame, or on a piece of hot iron, and allowing the joint to gradually cool.

Springy callipers are of two sorts, inside and outside. The making of a calliper belonging to either class is managed by forging it of one piece for both legs, and curving the mid portion to about a semi-circular form, to produce the required spring. This curving is effected on a steel filler of proper shape; and, after curving, the legs are filed and drilled to receive the adjusting screw. One end of this screw has a round hole drilled in, and swings on a pivot-pin which is tight in one calliper-leg, while the remainder of the screw extends through an oval hole in the other leg. In Fig. 547 a springy calliper's adjusting screw is shown by S, one end of the pivot-pin on which the screw swings is denoted by P, and the oval hole, to permit the swinging movement of the screw, is indicated by H.

The feet or points of all small callipers require hardening; this is effected by heating them to redness in a gas-flame and cooling them in oil, and allowing them to remain without any future tempering, or by cooling them in water, and afterwards tempering them to a blue colour. When cooled in water, the tempering is effected by polishing the point with emery-cloth, and holding the mid portion of the leg in the gas-flame until the blue colour appears at about a sixteenth of an inch from the extremity, at which time the leg is cooled to prevent farther softening. Hardening of calliper-ends should be performed after the calliper is finished and riveted together.