After drilling, and while the dies are fixed, without loosening the packing, the screwing should be done with a long taper tap. This is easily accomplished with small dies, by screwing the tap into both ends of the hole, and reversing the dies a few times, as directed for tapping a plate. Large dies require a partial screwing with a hob, and when the die-thread is shaped with the hob to nearly the complete shape, the long taper tap is slowly screwed through without any need of stopping to enter the tap into the opposite side. The hob which is used for such screwing is employed while the dies are loose, without the packing-piece, and the hob is screwed tight between the dies by means of the adjusting screw. During this screwing the hob's head is gripped in a vice, while the frame and dies are revolved around, if the frame is of sufficient length; if not, it is gripped in the vice and the hob is rotated with a tap-wrench. In this process the thread is formed into the dies by the gradual closing together of the dies towards each other, by working the adjusting screw, and when the thread is nearly full, the hob is taken out, and the dies are screwed together with the packing tight between, that the long taper tap may be screwed through in an easy manner without risk of breaking any of its teeth through rotating it backwards.

The final polishing of a pair of die-screws is easily effected with smooth hobs, termed screwers for dies, which are shown by Figs. 380 and others. These tools are of various diameters, although they may have similar threads, for the convenience of using them to make threads of the same shape into dies of various sizes, dies of different dimensions being necessary for screwing rods and bolts that greatly differ from each other in diameter, although it may be requisite to screw all of them with threads of the same step and shape. A screwer of this class should not be parallel, but thickest about mid way between each end of the screw, the difference of diameter being about a fiftieth of the hob's greatest diameter. All such hobs require a greater length of screw than is necessary for a hob that is to be used merely as a standard, or for shaping a screw-tool, the extra length of screw being required to gradually advance the thickest part of the hob into the work, instead of suddenly, which would rough the thread instead of smoothing it. The mode of using a hob of this class for screwing dies, consists in screwing it slowly through with plenty of oil, while the dies are screwed tight with the packing between. If, after such screwing the thread is seen to be rough, the packing is taken out and filed thinner, and again put between and screwed tight; after this, the hob is again slowly screwed through with oil, and the thread is again examined, to discover if further smoothing is needed; if so, another small quantity is filed off the packing, and the hob again screwed through as before. When sufficiently smoothed, it becomes ready for polishing, and this is effected by cleaning off all oil that was used for screwing, and rotating the screwer to and fro while an abundance of soapy water is applied for lubrication, instead of oil. Only the thick mid-part of the screw is used for this final polishing, and the hob is rotated to and fro in the hole until it begins to loosen, at which time the thread is probably polished; if not, a minute quantity is filed off the packing, and the thick part of the hob-screw is again screwed to and fro as before.

By these processes it may be inferred that it is not necessary to adjust die-screws to any precise diameter, and this is the fact, because one pair of dies may be adjusted to any precise distance from each other that may be necessary, by means of the adjusting screw, during the screwing of a rod, bolt, or other piece of work; but although the adjustment of die-screws to a precise diameter or depth is never requisite, there are a few things to observe connected with the cutting capabilities, and, therefore, their future usefulness. Consequently, it is proper to mention a few circumstances that are usually forgotten in die-making.

Every pair of dies whose screw is finished with a hob of the same thickness as the bolt to be screwed with the dies, possesses good cutting properties, because the cutting of the bolt is free, and is free through only a small quantity of the die-screw bearing on the bolt at the time of cutting. At the beginning of screwing is the greatest freedom, the bearing surface being then very small, as represented by the contact of the dies with a bolt in Fig. 605. As the dies are gradually forced together to cut the screw, the bearing surface increases, and continues to increase until the conclusion of the screwing; but at the same time the cutting capabilities decrease, and at the conclusion the dies are in contact with the circumference of the bolt, as shown in Fig. 606. In this situation the dies cut little or nothing, unless the hob which finished the dies were a little smaller in diameter than the diameter of the bolt being screwed; if so, the dies will entirely screw the bolt to its finished diameter without causing the bolt-screw to bear on the bottoms of the die-gaps ; therefore, to secure good cutting properties, a small hob for finishing the die-screws is requisite. Dies thus made are especially useful for small screws in general, such as those not more than about an inch in diameter. The greater the cutting properties of dies, the greater is the care required while using them to prevent them getting out of position and tearing the bolt-screw while being screwed; consequently, it is proper to put such tools into the hands of careful men.

A pair of dies which are finished with a master-tap possesses comparative inferior cutting properties, because the curves of the gaps in the dies are of greater angle than the curve of the bolt's surface to be screwed; or if not of greater angle, it is about the same. Master-tap dies may be made to cut only at the bottoms of the die-gaps, if the master-tap for finishing the dies is large enough in diameter. Such dies are often screwed with a hob which is as thick at the bottom of the thread as the outer diameter of the bolt to be screwed, by which means the bottom of the die-screw is made to bear entirely on the bolt at the commencement of screwing, and a firm steady bearing is thus obtained without much cutting property. Dies finished with such a hob cannot cut much at the outer edges, because the large curve of the die-gap causes the bolt to bear at the bottom of the gap when the screwing begins, and through this contact being effected most of the blunt character of such dies arises. It is to secure the steady bearing while cutting that dies made with master-taps are used, because little or no care is necessary to use them, through the firm grip which is given immediately the dies are screwed tight to the bolt. Probably it is better to sacrifice a little of the firm bearing quality, and to secure a power for cutting, because for nearly all the screws that are made with dies, an accurate thread is not required; superior threads are always expected from lathe-screwing, not from dies; therefore dies made with small hobs are preferable for most of the general screw-making when dies are the instruments employed.