Die-nuts resemble screwed plates with regard to their action while in use, but not in the objects to which they are applied. Screwed plates are never used for screwing a rod, bolt, or other piece of work which is more than half an inch thick, but a die-nut is useful for screws that may be two or three inches thick. The height of the die-nut may be about one and a half times the thickness of the screw to be adjusted, a long bearing in the nut being allowable because only a very thin shaving is to be cut off while adjusting. A die-nut is of but little use if its screw is not tapered at one end of the hole; if its hole is parallel, and many of them are so, the few cutting edges around the mouths of the hole soon become blunt, and therefore soon require softening, sharpening, and hardening; but if one end of the hole is tapered, the nut will remain serviceable for cutting off the very thin shavings for which it is made, during several years without sharpening.

The tools required to grip die-nuts while in use, are gap-spanners, die-frames, or plates and bolts ; a die-nut may also be forged solid with a handle, or forged in the shape of a tap wrench, having one or two screwed holes in the mid portion of the implement. A tool of this sort is especially useful if all the adjustment to be done with it is to be performed with the two hands while the screws to be adjusted are held by a vice. It is not often necessary to adjust screws in this manner, so that such nuts solid with handles are seldom wanted; the ordinary shape of the outer sides of die-nuts are usually similar to the outer sides of other nuts, so that they may be easily gripped with spanners, when it may be necessary to adjust screws while they rotate in lathes.

The drilling of such a nut requires care, to prevent the hole being made too large, and to produce a full thread without making the hole too small. When drilled, the screwing is properly done with a long taper tap having sharp teeth; and if the nut is for screws only about a quarter or three-eighths of an inch thick, the screwing of the die-nut, or gauge-nut as it is often named, may be managed by carefully using only one tap; but whenever more than one tap can be used for one hole, they should be employed if of a proper diameter, whether the die-nut being tapped is small or large. The final screwing of a nut of this sort, may also be easily done with a hob which is properly tapered to make it thickest in the mid part, such as were mentioned for the die-screwing and screwed plates. Whether long taper taps, hand taps, or proper hobs are employed for finishing die-nuts, it is quite necessary that the hob or tap for finally screwing the hole, should be only a very small amount thicker than the tap or hob that was put through next previous, because the screw cannot be smoothed unless a very small quantity only is taken out by the hob or tap; hence arises the necessity of providing hobs or taps that differ from each other in diameter only about a hundredth of an inch, but having threads of the same step and shape.

Large nuts of this class need a very gradual rotation of the tap or hob, also several back-ward rotations to release the tap and enter it from opposite sides, for if the tap is advanced until it becomes tight, the rotation backwards will break off some of the tap's teeth. The tap or hob used for finishing requires to be screwed through the nut two or three times from both ends of the hole, and if after such treatment, the screw is still rough, through blunt teeth, or through the hob cutting out too much, the remedy is to heat the nut to a dull red heat and harden it, which will make the hole smaller; the nut is next softened, and the hob or tap is again screwed through, after which, the hole may be again made smaller, by another heating, if required. The holes in screwed plates also, may be reduced in a similar manner.

The oil-channels are formed by drilling three, five, or seven cylindrical holes at equal distances around the screwed hole, being careful to mark the places at a proper distance to prevent the drill breaking through the thin side into the thread. After drilling, each channel is filed smoothly and its thin side filed out, to produce wide openings into the screwed hole and to smooth the edges; these openings also reduce the bearing surface of the thread, in addition to providing room for oil and shavings. The shavings will never at any time occupy much room, but it is highly necessary to prevent friction of the screw by reducing the thread, so that only a small amount of surface shall be in contact with a screw which is being adjusted. After the channels or gaps are finished, the thin extremities of the thread require cutting off, to make the cutting surfaces of the teeth broad, this trimming being similar to that for dies and screwed plates.

The coning of the hole of a die-nut, should be first partly done with a rosebit previous to commencing the screwing, and afterwards completed with a smooth filing and scraping when the screw is finished and the channels made.

The hardening of a die-nut, especially a large one for adjusting screws two or three inches thick, should be done while at a very dull red heat, to avoid distortion. If the screw is put much out of its proper shape, the nut when used for adjustment, will probably injure the screw instead of improving it, either by making it too small, or by roughing the thread. It is therefore necessary to soften the nut if distorted sufficient to do harm, that the finishing hob or tap may be again screwed through, and the nut again hardened. To modify such bending or twisting here referred to, two or three preliminary softenings, and planings or filings, should be given

2 D 2 to the nut at the commencement of its making, but not till after the hole for the screw is bored; and the larger the nut, the greater is the need for such care. It is also proper to finish the screw of the die-nut with a tap or hob which is rather greater in diameter, than the required diameter of the screws that will be adjusted with the nut when it is finished.

It is now needful to close this chapter on tool-making, and it will be noticed that all definitions and descriptions that are not requisite, are omitted in these processes, for the sake of brevity, and to avoid explaining terms and peculiar tools at the time a process is detailed. For this reason a learner must refer to the definitions and sketches given in the second chapter, if not, the processes mentioned in the third one cannot be understood, except by machinists.