The Screw and Standards 1798-1851

One of the six ancient machines, the screw, which is an inclined plane wrapped around a cylinder, has been in use for thousands of years. However, consistent reproduction and standardization of thread forms is relatively recent, being formalised between the 1840 and 1950. Nonetheless, as Abraham Rees, author of the Cyclopaedia ; or, Universal Dictionary of Arts, Sciences, and Literature (1802-20) wrote 'Screws are, of all the mechanical powers, the most frequently used in machines'. There was a problem though; screwthreads with their combinations of thread angle, pitch, diameter, depth and form were bespoke before standardization. The engineer James Nasmyth summarized the problem: 'all bolts and their corresponding nuts had to be marked as belonging to each other; and any mixing of them together led to endless trouble, hopeless confusion, and enormous expense' (James Nasmyth, Engineer [1883]). The adoption of the leadscrew lathe—made famous by Henry Maudsley in 1798— allowed for mechanical reproduction of thread-forms, which meant that, for the first time, nuts and bolts could be made in different locations and still fit together. Linking the adoption of screw forms to the tolerances adopted for flatness in the nineteenth century, and to the standardization of poetic forms, I will discuss texts including Joseph Whitworth's ‘Plane Metallic Surfaces’ (1840); Whitworth's ‘On a Uniform System of Screw Threads’ (1841); and Coventry Patmore's 'English Metrical Critics’ (1857). I will argue that behind the official standards on threads, flatness and poetic form that arose in the mid-C19 lies vernacular knowledge and practice.