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Dating old screws

Early nails were usually square in section and the earliest were individually forged by hand from iron.

The head of the nail was formed either by simply turning it over to form an L-shape or by striking a hand-held mould or 'bore' over the end of the shank to produce a shaped end such as a 'rose-head', a simple four sided pyramid shape.

Early lathes, many centuries ago, were not adapted to screw-cutting.

Later, from the Late Middle Ages until the early nineteenth century, some lathes were distinguishable as "screw-cutting lathes" because of the screw-cutting ability specially built into them.

A screw-cutting lathe is a machine (specifically, a lathe) capable of cutting very accurate screw threads via single-point screw-cutting, which is the process of guiding the linear motion of the tool bit in a precisely known ratio to the rotating motion of the workpiece.

The ornamentation, though, tends to be done more by hand on older chairs, so on close examination, you’ll see subtle differences from one bit of ornamentation to another, or even the occasional chisel mark from a craftsman.Bars of the requisite thickness were then made into nails and spikes by 'nailers'.Only the head and the point were forged, so these nails, which were common from the 17th to the early 19th century, can be distinguished from earlier ones by the sharp regular profile of the cut section.Since then, most metalworking lathes have this ability built in, but they are not called "screw-cutting lathes" in modern taxonomy. Archimedes devised the water screw, a system for raising water.Screws as mechanical fasteners date to the first century BCE.

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Although screws were tremendously useful, the difficulty in making them prevented any widespread adoption.

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