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The taper rate for all NPT threads is 1 inch of diameter in 16 inches of length (3 ⁄ 4 inch per foot or 62.5 millimeters per meter) measured by the change of diameter (of the pipe thread) over distance of thread.
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. More screw threads are produced each year than any other machine element. [1] Threads are generally produced according to one of the many standards of thread systems.
The standard designation for a UTS thread is a number indicating the nominal (major) diameter of the thread, followed by the pitch measured in threads per inch.For diameters smaller than 1 / 4 inch, the diameter is indicated by an integer number defined in the standard; for all other diameters, the inch figure is given.
For a taper thread, it is the diameter at the "gauge length" (plus/minus one thread pitch) from the small end of the thread. The taper is 1:16, meaning that for each 16 units of measurement increase in the distance from the end, the diameter increases by 1 unit of measurement.
Both British standard and National pipe thread standards specify a thread taper of 1:16; the change in diameter is one sixteenth the distance travelled along the thread. The nominal diameter is achieved some small distance (the "gauge length") from the end of the pipe.
Nominal Pipe Size (NPS) is a North American set of standard sizes for pipes used for high or low pressures and temperatures. [1] " Nominal" refers to pipe in non-specific terms and identifies the diameter of the hole with a non-dimensional number (for example – 2-inch nominal steel pipe" consists of many varieties of steel pipe with the only criterion being a 2.375-inch (60.3 mm) outside ...
Below is the historical thread size table, not to be confused with G threads, which are actually in use as British Standard Pipe. For example a G½ (half inch) is 20.955mm in diameter. For example a G½ (half inch) is 20.955mm in diameter.
Such an appropriately sized drill is called a tap drill for that size of thread, because it is a correct drill to be followed by the tap. Many thread sizes have several possible tap drills, because they yield threads of varying thread depth between 50% and 100%. Usually thread depths of 60% to 75% are desired.