Thread Forms and Terminology
The invention of the screw thread is attributed to Archimedes in the 3rd Century BC. The Archimedes Screw consisted of a cylinder with an internal continuous screw thread. When the lower end was placed into water and the cylinder rotated, water was raised to a higher level. The principle was also applied for handling light, loose materials such as grain, sand and ashes. The screws that we have today use the same technique in that a mating threaded component, rather than water, is moved through the cylinder.
Sir Joseph Whitworth, the British mechanical engineer, was well known for his work on engineering standards. In 1841, he proposed the introduction of standard fastener sizes to the Institution of Civil Engineers. These comprised of a universal set of specifications for the angle and pitch of screw threads. The Whitworth thread became the first standard thread system in the world.
A screw thread is a ridge of uniform section in the form of a helix on the external or internal surface of a cylinder. Threads on bolts, screws and studs are examples of 'external threads', while those in nuts or tapped holes are 'internal threads'.
There are so many types of thread sizes, pitches and tolerance classes in both metric and inch configurations that they require some definition and terminology for the specifier.
That's a snippet of the history of fasteners - in future contact us for technical advice and product selection for cost effective solutions.