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Pipe Sizes & Threading Information
BSP BSP thread form stands for British Standard Pipe and is common in Australia and the commonwealth countries. It is based on trade size rather than actual diameter which can lead to some confusion when measuring ports. There are two types of BSP threads; - Parrallel (BSPP) - also known as G or Rp - Tapered (BSPT) - also know as R or Rc Both threads have the same pitch, angle (55 degrees) and shape (rounded peaks and valleys). The below table gives the major and minor diameter for each BSP Trade Thread Size.
NPT NPT stands for National Pipe Thread and is an American standard thread. It may also be reffered to as MPT , MNPT or NPT (M) for male external threads and FPT, FNPT or NPT(F) for female interal threads. A thread sealant must always be used to achieve a leak free seal (except for NPTF). It is also based on Trade Size rather than actual diameter (similar to BSP in this regard). Both threads have the same pitch, angle (60 degrees) and shape (flat peaks and valleys). The below table gives the Threads Per Inch, Pithc and Major Diameter for NPT Threads.
BSP vs NPT NPT threads are common in the United States and a few other countries, BSP threads are widely used in many other countries. BSPT -British Standard Pipe Taper BSPP -British Standard Pipe Parallel NPT -National Pipe Taper NPS -National Pipe Straight While the actual specified outside diameters of American National Pipe differ slightly from those of British Standard Pipe, either thread may reliably be cut onto a pipe of its respective trade size. BSPT equivalent is NPT and BSPP’s equivalent is NPS. Never swap threads if it is a high pressure application. NPT/NPS and BSP threads are not compatible due to the differences in their thread forms, and not just the fact that most sizes have a different pitch. NPT/NPS threads have a 60° angle and have flattened peaks and valleys (Sellers thread form) where as BSP threads have a 55° angle and have rounded peaks and valleys (Whitworth thread form). NPT and BSP thread pitches (threads per inch) are listed below. To determine pitch, use a thread gauge or count the number of threads that fall into a 1" span.
In plumbing pipe size is referred to as nominal pipe size - NPS, or "Nominal Pipe Size". The metric equivalent is called DN or "diametre nominel". The metric designations conform to International Standards Organization (ISO) usage and apply to all plumbing, natural gas, heating oil, and miscellaneous piping used in buildings. The use of NPS does not conform to American Standard pipe designations where the term NPS means "National Pipe Thread Straight". ISO 6708 - Pipework components - Definition and selection of DN (nominal size) ISO 6708 defines the nominal size - DN - as an alphanumeric designation of size for reference purposes. It comprises the letters DN followed by a dimensionless whole number which is indirectly related to the physical size in millimetres of the bore (ID) or outside diameter (OD) of the end connections. Outside diameters for metric and imperial standards are indicated in the table below.
Pipe Sizes Derived from: Engineering Toolbox Pipes are made of a wide variety of materials - like galvanized steel, black steel, copper, cast iron, concrete, and various plastics such as ABS, PVC, CPVC, polyethylene, polybutylene and more. Pipes are identified by "nominal" or "trade" names that are loosely related to the actual dimensions. For instance, a 2-inch galvanized steel pipe has an inside diameter of about 2 1/8 inches and an outside diameter of about 2 5/8 inches.
D or (ID)Inside Diameter NPS - Nominal Pipe Size Dx - (OD) Outside Diameter
Pipe Threads Derived from various sources: 1) https://www.valvesonline.com.au/references/threads/ 2) https://www.plumbingsupply.com/pipethreadsizing.html National Pipe Threads (NPT) have tapered threads. These are the most common threads used for general purposes. NPT threads are designed with a 60 degree thread angle, and are used for joining and sealing pipe to fittings in low pressure air or liquids and also mechanical applications. The tapered thread is 3/4" over one foot of length. Tapered threads are deeper at the end of the pipe and are increasingly shallower the further they are from the end of the pipe. The taper on the pipe only allows the pipe to screw inside the fitting until it is forced to stop because of the taper. The distance the pipe can be screwed into the fitting is specified by the ANSI standard. After tightening with a wrench the threads may have slight spaces between the pipe and fitting which could cause a leak so a pipe sealant must be used to ensure any gaps are filled. The Dry-seal thread (NPTF) also have tapered threads. NPTF threads are used when the application is such that pipe sealing compounds may fail due to higher heat or pressure than normal NPT threads can withstand. The threads are designed to seal mechanically by slightly, but sufficiently, crushing the threads when tightened with a wrench. This allows for joining the pipe and fitting without sealants. The NPT and NPTF threads can be interchanged if sealants such as PTFE tape or suitable pipe joint compounds are used. None of the other thread standards are fully interchangeable (GHT, NST, BSPT, NPSI, etc.) Female NPT threads can be designated as "FPT" or "FIP" and male NPT threads can be designated as "MPT" or "MIP". National Standard Free-Fitting Straight Mechanical Pipe Threads (NPSM) have straight threads which are only used for joining. A washer or gasket is needed to seal this type of threaded connection. There are also three less common thread types used in the plumbing industry. The Garden Hose Thread (GHT) and the Fire Hose Thread (NST) have coarse threads. The seal is made with a gasket or washer and are used mainly for attaching (joining) hoses to valves quickly, without the use of a wrench. The British Standard Taper Pipe Thread (BSPT) has a 55 degree thread angle (NPT are 60 degree) and is used internationally as a standard thread for joining steel pipes.