Dies are employed for screwing rods and bolts, and are made in couples, termed pairs. Each pair of dies are required to make one class of screws, and a pair consists of two steel grips, having teeth on the gripping surfaces. The shapes and dimensions of these teeth are the same as of the required thread on the work, consequently .the grips are formed with teeth of various thicknesses, to make small screws and large ones. Each pair of dies are held while in use by means of a die-holder, or die-frame. A light class of die-frames are shown by Fig. 367, which indicates a pair of dies in their frame ready for use. One of the handles of this frame has a short screw, and also a hole; this hole admits one end of a short lever to work the screw in or out, by which the dies are closed together or separated to make the piece which is being screwed to a proper diameter. To allow the egress of shavings, dies are formed with gaps somewhat resembling the gaps in screwed plates; but the action of dies while in use is different to that of a screwed plate, because one hole in a plate will form screws of only one diameter, but one pair of dies will make screws of several different diameters, the precise diameter depending on the distance between the two dies while in use. This distance is shortened or lengthened to a minute degree by the dies being in their frame and adjusted by the adjusting screw which constitutes part of the handle. The point of this screw is in contact either with a packing block, or with the die which is nearest the screw point, and this die is the one which is pushed by the screw towards the other die that remains fixed at the bottom of the slot in the die-frame.

The die-frame denoted by Fig. 368 has a distinct screw for adjusting the dies; this arrangement being preferable for all large frames, in order that the adjusting screw may not be large, which is unavoidable with large handles having adjusting screws at their ends. Fig. 369 indicates another class of frames for large dies, having two adjusting screws ; in this frame the dies are held by two thin plates that are attached with six small screws; these screws are partly unscrewed whenever it is necessary to take out one pair of dies and put another pair into the die-frame. The slots in the frames shown by Figs. 367 and 368 are shaped to fit the angular gaps in the dies shown by Figs. 370 and 371 ; and the dies shown by Fig. 372 are shaped to one of the forms that are used for the frame 369. The six holes in the two plates of frame 369 are shaped to the outline of the figure 8, the smaller end of the hole being for the steins of the fixing screws, and the larger part being large enough to allow the heads of the screws to pass through ; by such means the two plates are slid along until the holes are opposite the screw-heads, and lifted off with merely loosening the screws about half a rotation.

The die-frame shown by Fig. 375 has but one plate for holding the dies; this plate is a little tapered, and also dovetailed in shape, which permits the plate to be gently driven into and out of its place whenever it is necessary to put in other dies. The plate or lid is shown by L, and is between the two guides, which are attached by six screws; these guide-plates are made distinct from the remainder of the frame, and fastened with screws, after which they remain fixtures. Fig. 376 denotes a frame which is fitted with a lid similar to that of Fig. 375, but has but one handle ; such a die-frame is especially adapted to hold dies for screwing by means of a lathe, and for holding die-nuts, that are denoted by Figs. 373 and 374. Fig. 377 shows a frame whose plate swings on a joint-pin when it is needful to take out a pair of dies and put another pair into their place. The two pairs of dies shown by Figs. 378 and 379 are in the shapes that are suitable for either of the frames indicated in Figs. 369, 375, 376, and 377.

The teeth on the gripping surfaces of dies are formed by hobs and master-taps, and afterwards by making the gaps for the shavings. A master-tap is a class of hob which is larger in diameter than the screws that will be made by the dies when screwed ; and by using both a hob and master-tap for screwing one pair of dies, one die is made with a larger curve in the gap than is given to the curve in the gap of the other die, by which means the die having the larger curve is made to act as a bearing while the other die is cutting. When it is convenient, the hob or master-tap is screwed into the dies to form the thread, instead of the dies and frame being revolved around the hob, which sometimes injures the thread. Dies are often screwed with a hob having straight grooves; one of this class is denoted by Fig. 380; and a die-screwer, which is rather taper instead of being parallel, is indicated by Fig. 381. In some hobs for die-making the grooves are not straight, but in the shape of screws; a tool of this class is denoted by Fig. 382.