TABLE OF CONTENTS The invention of the screw thread is arguably second in importance only to the invention of the wheel. Although there have been many developments in fastening technology since the invention of the screw thread, it remains as the primary method of securing parts in countless applications in almost every walk of life.
Screw threads cut by die plates and threaded holes cut by longitudinally grooved screws have been known for centuries. Primitive taps were cut by hand with no standardisation of pitch being possible. An attempt to try to standardise thread pitches and diameters was made by Holtz Apfel, a mechanic who was in business in the Charing Cross area of London in the nineteenth century.
Others also became involved in trying to standardise thread forms, but it was left to Sir Joseph Whitworth in a paper read before the Institution of Civil Engineers on 15 June 1841 to introduce a formal standardisation system based on a 55 flank angle. In 1864 an American, William Sellars carried this standardisation procedure further by proposing the 60 flank angle, which was then adopted almost universally.
A major step forward in unification of screw threads was taken in 1898 by the International Conference held in Geneva resulting in the formulation of the Systeme International (SI) metric thread.
However, many different national thread standards have emerged since that time for various applications. These have today polarised into two main standards: The metric thread for Europe and the unified system in the...
