National Pipe Threads (NPT)
The physical dimensions of a Pipe are referred by the size of die, but standards of plumbing industry vary from the actual size and proportion of the Pipe. You should be conscious in the measuring of the pipe because mostly it can misguide you to choose the wrong material pipe. The “pipe thread size” as shown in column 3 is based on the inside of the pipe and measure on the value in the table. You must measure the outside diameter of each pipe for the actual identification of the size of the pipe. For example, there is an outside diameter of 3/4″ NPT pipe thread is 1.050 inches. Threads per inch (TPI) are defined for each thread size. There are 14 threads per inch in the 3/4″ NPT pipe thread. For definite classification of the thread, there is need of both the TPI (threads per inch) and OD (outside diameter) of the thread because several sizes have the same TPI.
Male threads: The significant portion of the thread should be measured from the outside diameter at “A”; in column 1 or 2 of chart find figure nearest this dimension. Your nominal pipe thread size will be the dimension in column 3
Female Threads: Top diameter of thread at “B” should be measured; In column 1 or 2 of chart find figure nearest this dimension. Your nominal pipe thread size will be the dimension in column 3
The American National Standard for pipe has specified all pipe thread types used in plumbing as accredited by the American National Standards Institute (ANSI).
NPT pipe thread is tapered threads. For general purposes usage, these are the most common threads. NPT threads are designed at an angle of 60-degree thread angle in the NPT threads, and they are used for joining and sealing the pipe. The tapered thread is 3/4″ over one foot of length. At the end of the pipe tapered threads are deeper and the further they are from the end of the pipe and are increasingly shallower.
The pipe is only allowed by the taper on the pipe to screw inside the fitting until it is forced to stop because of the taper. The ANSI standard specifies the distance the pipe can be screwed into the fitting. The threads may have slight spaces between the pipe and fitting after tightening with a wrench due to which a leak can be caused so for ensured about the gaps being all filled a pipe sealant must be used. Threads are also tapered by the Dry-seal thread (NPTF). When the usage is such that the pipe sealing compounds may malfunction due to higher heat or pressure than standard NPT threads can withstand at that point, NPTF threads are used.
When tightened with a wrench the threads are designed to mechanically seal, that allows crushing the threads. The joining of pipe and fitting without sealants is allowed by it. If sealants such as PTFE tape or suitable pipe joint compounds are used, then the NPT and NPTF threads can be interchanged. None of the other thread standards are fully interchangeable (GHT, NST, BSPT, NPSI, etc.). “FPT” or “FIP” can be the designation for Female NPT threads and “MPT” or “MIP” can be the designation for male NPT threads. There are straight threads in National Standard Free-Fitting Straight Mechanical Pipe Threads (NPSM) which are only used for joining.
There is need of a washer or gasket to seal this type of threaded connection. The usage of these three thread types is also very common in the plumbing industry. There are coarse threads in the Garden Hose Thread (GHT) and the Fire Hose Thread (NST). A gasket or washer is used to make t and is used mainly for attaching (joining) hoses to valves quickly, without the usage of a wrench. There is a 55-degree thread angle in the British Standard Taper Pipe Thread (BSPT) (NPT are 60 degrees), and it has a standard thread for joining steel pipes which are its international usage.
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