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The taper on NPT threads allows them to form a seal when torqued as the flanks of the threads compress against each other, as opposed to parallel/straight thread fittings or compression fittings in which the threads merely hold the pieces together and do not provide a seal.
A screw thread, often shortened to thread, is a helical structure used to convert between rotational and linear movement or force. A screw thread is an inclined plane wrapped around a cylinder or cone in the form of a helix, with the former being called a straight thread and the latter called a tapered thread.
Note: the straight iron pipe thread is a temporary connection and seals with a gasket, just like garden hose threads and fire hose threads, and is distinct from tapered iron pipe thread (NPT), which is a permanent connection sealed by the threads in conjunction with pipe dope or teflon tape wrapped around the threads.
An example of this is a "3 ⁄ 4-inch female adapter NPT", which would have a corresponding male connection of the same size and thread standard (in this case also NPT). Common piping and plumbing fittings
The Unified Thread Standard (UTS) defines a standard thread form and series—along with allowances, tolerances, and designations—for screw threads commonly used in the United States and Canada. It is the main standard for bolts, nuts, and a wide variety of other threaded fasteners used in these countries.
The seal provided by a threaded pipe joint depends upon multiple factors: the labyrinth seal created by the threads; a positive seal between the threads created by thread deformation when they are tightened to the proper torque; and sometimes on the presence of a sealing coating, such as thread seal tape or a liquid or paste pipe sealant such ...
Taper threads, British Standard Pipe Taper thread (BSPT), whose diameter increases or decreases along the length of the thread; denoted by the letter R. BSPT threads [2] These can be combined into two types of joints: Jointing threads These are pipe threads where pressure-tightness is made through the mating of two threads together.
The most common pipe thread in North America is the National Pipe Thread (NPT) or the Dryseal (NPTF) version. Other pipe threads include the British Standard Pipe Thread (BSPT), the garden hose thread (GHT), and the fire hose coupling (NST). Copper pipes are typically joined by soldering, brazing, compression fittings, flaring, or crimping.