National pipe thread

National Pipe Thread Taper (NPT) is a U.S. standard for tapered threads used on threaded pipes and fittings. In contrast to straight threads that are found on a bolt, a taper thread will pull tight and therefore make a fluid-tight seal. In 1864, William Sellers, being the president of Franklin Institute, presented a standard for nuts, bolts and screws, which became the National Pipe Tapered (NPT) thread.