National Pipe Thread

in Pipe

Pipe thread sizes



Nominal



NPT Size



Outer



Diameter



inch (mm)



Threads



per inch



Pitch



of Thread



inch (mm)



1/16"



0.3125 in (7.94 mm)



27



0.03704 in (0.94082 mm)



"



0.405 in (10.29 mm)



27



0.03704 in (0.94082 mm)



"



0.540 in (13.72 mm)



18



0.05556 in (1.41122 mm)



3/8"



0.675 in (17.15 mm)



18



0.05556 in (1.41122 mm)



"



0.840 in (21.34 mm)



14



0.07143 in (1.81432 mm)



"



1.050 in (26.67 mm)



14



0.07143 in (1.81432 mm)



1"



1.315 in (33.40 mm)



11



0.08696 in (2.20878 mm)



1"



1.660 in (42.16 mm)



11



0.08696 in (2.20878 mm)



1"



1.900 in (48.26 mm)



11



0.08696 in (2.20878 mm)



2"



2.375 in (60.33 mm)



11



0.08696 in (2.20878 mm)



2"



2.875 in (73.02 mm)



8



0.12500 in (3.175 mm)



3"



3.500 in (88.90 mm)



8



0.12500 in (3.175 mm)



4"



4.500 in (114.30 mm)



8



0.12500 in (3.175 mm)



5"



5.563 in (141.30 mm)



8



0.12500 in (3.175 mm)



6"



6.625 in (168.27 mm)



8



0.12500 in (3.175 mm)



10"



10.750 in (273.05 mm)



8



0.12500 in (3.175 mm)



12"



12.750 in (323.85 mm)



8



0.12500 in (3.175 mm)



14" OD



14 in (355.60 mm)



8



0.12500 in (3.175 mm)



16" OD



16 in (406.40 mm)



8



0.12500 in (3.175 mm)



18" OD



18 in (457.20 mm)



8



0.12500 in (3.175 mm)



20" OD



20 in (508.00 mm)



8



0.12500 in (3.175 mm)



24" OD



24 in (609.60 mm)



8



0.12500 in (3.175 mm)



Sometimes these terms may be used:



MIP: stands for Male Iron Pipe, or Male International Pipe, or MPT Male Pipe Thread. It is a term for pipe fitting.



FIP: stands for Female Iron Pipe, or Female International Pipe, or FPT. It is a term for pipe fitting that fit into MIP.



COMPRESSION fitting is a different type of fitting than MIP FIP fitting, COM or CMP. It has 1 5/8" per inch taper, more than FIP.



FLARE fitting: a fitting that has tapered smooth tip, then threaded body. The Male flare fitting will require a female flare fitting. It is usually found in gas line connection, where a tight smooth sealed surface is required.



IPS: Iron Pipe Size thread. Even though the word "Iron" may be used in these abbreviations many materials used are other metals, alloys, or plastics. IPS is taken same as MIP.



Garden Hose:



The difference between FIP MIP and Compression fitting is in the tapering of the thread. FIT has 3/4" per foot taper, or only 1/16" per inch taper; Comp has 1 5/8" per foot, or only 13/96" per inch taper.



A compression fitting has a normal thread (like a screw) and relies on a ferrule (an olive shaped soft copper sleeve) or more commonly a tap washer (fibre or rubber) to provide a watertight seal. For attaching to most taps (plastic or steel) compression fittings are used, and remember to put a washer on! Normally the male threaded member has a blunt end that the washer sits against. Or if it's to fit to a copper pipe, you stick on an olive, which is compressed against the pipe by the adjacent conical seats in the fitting when it is tightened, and holds the pipe watertight. The tubing for compression is usually straight, but the female and male part of fittings thread are also tapered, more taper than FIP MIP. For compression fitting, the taper is 1 5/8" per 1 inch taper. For a 5/8 compression, the inside will be 3/16, the outside will be 23/32" for a distance of 3/16".



A female iron connection has a tapered thread - which thins out to the end of the pipe. As you tighten against it, the ever-decreasing thread depth means that the connection becomes watertight. You'd not use an olive or washer here - instead you use a bit of PTFE tape (polytetrafluoroethylene) wrapped around the thread. So for attaching to radiator bodies you normally have this sort of joint, where you have a hard (non-malleable) material to join to. It requires the opposite end to be MIP.



MIP fittings are usually found in big strong thick copper pipe , iron pipe, steel pipe, gas pipe, gas stove, gas oven, gas heater, gas water heater connection.



Sometimes a household sink tap does not come with a FIP thread end. In the UK - it's normally a standard BSP 1/2" or 3/4" end.(British Standard Pipe). Sometimes it is MIP FIP end. Before 1980, most water plumbings are done with metal fittings (copper, brass, aluminum, soft iron) which compress. Most household wall On-Off-valve (2 in above floor) to bathroom toilet, wash basin sink, kitchen faucet are designed for metal compressible tubing. Thus on-off valves are usually Compression fittings. Before 1980, some (small percentage) wash basin faucets bottom have thick copper metal pipe 2" long, non-compressible, but tapered MIP (very obvious taper). They need FIP fitting connector hoses. After 1980, most faucets are IPS ABS material (strong, hard, durable plastic) and slight tapered, but still have MIP and requires FIP fitting hose on faucet. (1/2" FIP on faucet end). Old faucet with copper tubings from faucet may be 5/8 female compression. Thus a 5/8 male compression to 1/2 MIP fitting adapter (5/8 m-CMP - 1/2 MPT) may be needed. The 5/8 m-comp end is for the wall on-off-valve welded tubing. The 1/2 FIP end is for new hose to 1/2 FIP faucet end. Sometimes old 5/8 might be 1/2, and may need 1/2 m-comp-1/2 MIP instead of 5/8 m-comp-1/2 MIP.



References



Oberg, Erik; Franklin D. Jones, Holbrook L. Horton, and Henry H. Ryffel (2000). ed. Christopher J. McCauley, Riccardo Heald, and Muhammed Iqbal Hussain. ed. Machinery's Handbook (26th edition ed.). New York: Industrial Press Inc.. ISBN 0-8311-2635-3. 



See also



AN thread



British standard pipe thread



Pipe fitting



Plumbing



Taps and dies



Threaded pipe



Unified Thread Standard



External links



Newman Tools Inc. and J.W. WINCO, INC. show the Whitworth form BSP or ISO pipe thread.



How much should you tighten a NPT fitting?



National Standard Taper pipe Threads Sizes Chart



Categories: Drilling and threading | Mechanical standards | Piping | PlumbingHidden categories: Articles needing additional references from July 2009 | All articles needing additional references | Articles needing cleanup from July 2009 | All pages needing cleanup

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This article was published on 2010/10/09