Slide-rest screwing tools include those for outside threads, and those that are necessary for inside threads. The implements for outside screwing are these: one-tooth vee-tools, one-tooth tools having straight cutting edges instead of vees ; also vee-tools having two or three teeth, and springy tools having two or three teeth. For inside threads a tool is used which nas a single tooth that is solid with the remainder of the tool; a small tool having one tooth which is distinct from the holder is also used for inside threads, this tool being keyed to its holder when necessary. Another class of small instruments for inside threads are those which have two or three teeth, and are keyed to their holders in the same manner as the one-tooth tools. A straight tool having a vee-tooth for outside threads is denoted by Fig. 440, and one with a similar tooth, but cranked, is shown by Fig. 441, the crank being necessary for corners which will not admit a straight tool. Screw tools having two teeth are denoted by Fig. 442 ; one of this shape is employed after a one-tooth tool has cut out about five-sixths of the thread-groove; and after a straight tool with two or three teeth has smoothed and nearly finished the thread, a springy tool is used for a final polishing; one of this class is indicated by Fig. 443.

Inside threads are made with tools shown by Figs. 444, 445, 446, 447, and 448. The tool shown by Fig. 444 has a tooth extending from one side and solid with the remainder of the implement; this is only used for small holes that will not admit a stronger tool. The small tools named dents, are indicated by Figs. 445, 446, and 447; these are effectual for screwing all holes that are large enough to admit the dent while fastened in its holder; one of these holders is shown by Fig. 448, having a slot in which the dent is keyed ready for use. A dent whose cutting part is made to extend beyond the extremity of the holder is a cranked one, and denoted by Fig. 446 ; a tool of this shape is required when it is necessary to screw a hole having a bottom. A cranked dent-holder, which is so shaped to make it suitable for some sorts of slide-rests, is represented by Fig. 449.