In the nineteenth century, many different types of screw threads were required for hydraulic and pneumatic circuits as well as fastening components. As a result, manufacturers started to devise their own fastening systems. This resulted in compatibility problems.
The English mechanical engineer and inventor, Sir Joseph Whitworth devised a uniform threading system in 1841 to address the incompatibility problem. The Whitworth thread form is based on a 55-degree thread angle with rounded roots and crests.
This form was selected as a connecting thread for pipes, which was made self sealing by cutting at least one of the threads on a taper. This became known as the British Standard Pipe thread (BSP Taper or BSP Parallel thread). The Whitworth thread is now used internationally as a standard thread for jointing low carbon steel pipes.
In America, William Sellers set the standard for nuts, bolts, and screws which became the National Pipe Tapered Thread (NPT) in 1864. His 60-degree thread angle helped form the American Industrial Revolution, and later became the American National Standard.
The best known and most widely used connection where the pipe thread provides both the mechanical joint and the hydraulic seal is the American National Pipe Tapered Thread, or NPT. NPT has a tapered male and female thread which seals with Teflon tape or jointing compound.