The metal screw stayed a rarity for centuries, until factories made 16,000 a day
In the 1780s a Staffordshire wood-screw works turned out 16,000 screws a day with just 30 workers, a staggering output at the time. Before machines like theirs, each metal screw was filed by hand, with uneven threads and a blunt tip. That is why screws were almost unknown as fasteners for centuries.
People held things together for millennia with dowels, pegs, dovetails, nails, forge welds and knotted cord. Wooden screws did useful work in olive and wine presses around the Mediterranean by the 1st century BC, but Europeans seldom, if ever, fastened things with metal screws until the 1400s. The screwdriver first shows up in a manuscript from Wolfegg Castle written between 1475 and 1490, and probably did not become common until after 1800.
Two lines of invention met in the late 18th century. Brothers Job and William Wyatt patented a screw-making machine in 1760, guiding the cutter with a leadscrew and slotting heads with a rotary file. Their factory opened in 1776 and failed, but its new owners made it hugely productive. Meanwhile instrument maker Jesse Ramsden produced a satisfactory screw-cutting lathe in 1777, and Henry Maudslay's lathes of 1797 and 1800 brought precision threading to industry. America's turret lathes of the 1840s and automatic screw machines of the 1870s drove prices down again.
Screw heads have their own saga. Slots, squares and hexagons dominated the 19th century; clever alternatives were patented but proved too costly to make. In 1908 the Canadian P. L. Robertson found the exact taper that let a square socket be stamped cleanly into cold metal, and the hex socket followed in 1911. Henry F. Phillips popularised his cross-shaped drive in the early 1930s, later refined into Pozidriv and Supadriv.
Making a screw today takes three steps: cut wire into blanks, press the head cold with almost no waste, then roll the threads before coating against rust. Rolled threads are stronger because they do not sever the metal's grain. And a few screws turn the wrong way on purpose: a bicycle's left pedal uses a left-hand thread so pedalling does not unscrew it.
Source: Screw
