Screw-nails

Screw-nails, called in the trade 'wood screws,' are made from mild steel and iron; or from brass, copper, and zinc, when others would be destroyed by rust. Wood screws were in use long before the year 1760, when the brothers Wyatt obtained a patent for cutting screws by machinery. Before 1817, wood screws, being nearly all forged and then shaped by hand, were very expensive; but at that time a patent was granted to John Colbert, a German watchmaker, who made the first automatic machinery for this purpose. In the year 1854 a greatly improved machine was introduced from America, which may be said to have revolutionised screw-making. These machines are complicated, and expensive in first cost and also to keep in operation. The wire is supplied to the heading-machine, which cuts off a piece, and a blow from a die stamps a head on it. It is then turned and nicked, after which, in a worming-machine, a cutter passes several times along the blank and forms the thread and gimlet point. One person can attend to several of these machines. Considerable success has been attained in rolling the threads on screw blanks. Two reciprocating plates, or revolving discs, are made from hard steel, and grooved at an angle; the screw blank is rolled between them under great pressure, receiving the reverse impression of the grooves which form the thread. The annual consumption of wire for making wood screws in England amounts to 9000 tons. They are principally made in Birmingham, and one firm alone can produce 150,000 gross weekly.