leadscrew, the slide rest, gears, slide rests geared direct to spindles, and "change gear" gear trains) were developed over the centuries, with some of those elements being quite ancient. Various sparks of inventive power during the Middle Ages and Renaissance combined some of these elements into screw-making machines that presaged the industrial era to follow. For example, various medieval inventors whose names are lost to history clearly worked on the problem, as shown by Wolfegg Castle's Medieval Housebook (written circa 1475–1490), and Leonardo da Vinci and Jacques Besson left us with drawings of screw-cutting machines from the 1500s; not all of these designs are known to have been built, but clearly similar machines were a reality during Besson's lifetime. However, it was not until 1760–1800 that these various elements were brought together successfully to create (in contemporaneous parallel) two new types of machine tool: the screw-cutting lathe (for low-volume, toolroom-style production of machine screws, with easy selection of various pitches) and the first high-volume-production, specialized, single-purpose machine tools for the production of screws, which were created to produce wood screws [meaning screws made of metal for use in wood] at high volume and low unit price. Screw-cutting lathes fed into the just-dawning evolution of modern machine shop practice, whereas the wood-screw-making machines fed into the just-dawning evolution of the modern hardware industry, that is, the concept of one factory supplying the needs of thousands of customers, who consumed screws in growing quantities for carpentry, cabinet making, and other trades, but did not make the hardware themselves (purchasing it instead from capital-intensive specialist makers for lower unit cost than they could achieve on their own). These two classes of machine tools simultaneously took the various classes of screws and moved them, for the first time, from the category of expensive, hand-made, seldom-used objects into the category of affordable, often-interchangeable commodity. (The interchangeability developed gradually, from intra-company to inter-company to national to international). Between 1800 and 1840, on the machine-screw side, it became common practice to build all of the relevant screw-cutting machine elements into engine lathes, so the term "screw-cutting lathe" ceased to stand in contradistinction to other metalworking lathe types as a "special" kind of lathe. Meanwhile, on the wood-screw side, hardware manufacturers had developed for their own in-house use the first fully automatic [mechanically automated] special-purpose machine tools for the making of screws. The 1760–1840 development arc was a