Editing National pipe thread

{{Short description|U.S. national technical standards for threads on pipes and pipe fittings}}
[[File:Malefemalepipe.jpg|thumb|Threaded pipe and [[Piping and plumbing fittings#Elbow|elbow]]. The pipe has a [[Gender of connectors and fasteners|male]] NPT thread, while the elbow is [[Gender of connectors and fasteners|female]].]]
'''American National Standard Pipe Thread''' standards, often called '''national pipe thread''' standards for short, are United States national [[technical standard]]s for [[screw thread]]s used on [[threaded pipe]]s and [[Piping and plumbing fitting|pipe fitting]]s. They include both [[screw thread#Taper|tapered]] and straight thread series for various purposes, including rigidity, [[pressure]]-tight sealing, or both.{{sfnp|Machinery's Handbook|1996|pages=1772–1781}} The types are named with a full name and an abbreviation, such as '''NPT''', '''NPS''', '''NPTF''', or '''NPSC'''.

'''MIP''' is an abbreviation for male iron pipe, and '''FIP''' is an abbreviation for female iron pipe.<ref>{{cite book | last = Cauldwell | first = Rex | title = Plumbing | publisher = Taunton Press | location = Newtown, CT | year = 2006 | isbn = 1561588172 }}
</ref>

Outside North America, some US pipe thread sizes are widely used, as well as many [[British Standard Pipe]] threads and [[International Organization for Standardization|ISO]] 7–1, 7–2, 228–1, and 228-2 threads.

==Types==
The various types are each named with an abbreviation and a full name, as follows:{{sfnp|Machinery's Handbook|1996|pages=1776–1778}}

{| class="wikitable sortable" border="1"
|-
! scope="col" style="width: 16%;" | Abbreviation{{sfnp|Machinery's Handbook|1996|pages=1776–1778}}
! scope="col" style="width: 25%;" | Shorthand expansion
! scope="col" style="width: 24%;" | Full name{{sfnp|Machinery's Handbook|1996|pages=1776–1778}}
! scope="col" style="width: 35%;" | Comment{{sfnp|Machinery's Handbook|1996|pages=1776–1778}}
|-
| NPT || National pipe taper || American National Standard Taper Pipe Thread || Tapered and needs thread sealant; for connections in nearly every type of service 
|-
| NPS || National pipe straight || American National Standard Straight Pipe Thread || For rigidity; sealable with o-ring or gasket; sometimes male straight is mated with female tapered for low-pressure sealing{{fact|date=February 2025}}
|-
| NPSC || National pipe straight–coupling ||  American National Standard Straight Pipe Thread for Couplings || For general [[coupling]]s
|-
| NPSF || National pipe straight–fuel and oil || Dryseal USA (American) Standard Fuel Internal Straight Pipe Thread  || Internal only, straight
|-
| NPSH || National pipe straight–hose || American National Standard Straight Pipe Thread for Hose Couplings || For [[hose coupling]]s 
|-
| NPSI || National pipe straight–intermediate || Dryseal USA (American) Standard Intermediate Internal Straight Pipe Thread || Similar to NPSF but slightly larger; internal only, straight
|-
| NPSL || National pipe straight–locknut ||  American National Standard Straight Pipe Thread for Loose-fitting Mechanical Joints with Locknuts || For use with [[locknut]]s
|-
| NPSM || National pipe straight–mechanical ||  American National Standard Straight Pipe Thread for Free-fitting Mechanical Joints || For various rigid mechanical uses 
|-
| NPTF || National pipe taper–fuel and oil || Dryseal USA (American) Standard Taper Pipe Thread || For dryseal connections in nearly every type of service, especially [[fuel]] connections
|-
| NPTR || National pipe taper–railing || American National Standard Taper Pipe Thread for Railing Joints  || For [[handrail|railing]]s
|-
| PTF-SAE SHORT || Pipe taper, fuel, SAE, short || Dryseal SAE Short Taper Pipe Thread || Named after [[SAE International]]; similar to NPTF but one turn shorter
|}

== Uses ==
Threaded pipes can provide an effective seal for pipes transporting [[liquids]], [[gases]], [[steam]], and [[hydraulic]] fluid.  These threads are now used in materials other than steel and brass, including [[Polytetrafluoroethylene|PTFE]], [[Polyvinyl chloride|PVC]], [[nylon]], [[bronze]], and [[cast iron]].

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 fitting]]s in which the threads merely hold the pieces together and do not provide a seal. The various types of pipe threads are designed for use both with or without thread sealants,{{sfnp|Machinery's Handbook|1996|pages=1772–1781}} as particular applications demand. The sealants, where used, are typically [[thread seal tape]] thread sealant or a thread seal paste [[pipe dope]] (sometimes similar in composition to [[plumber's putty]]).

Because the thread body is tapered ({{convert|0.75|in/ft|1|abbr=on|disp=or}}), a larger diameter keeps compressing into a smaller diameter and finally forms a seal (no clearance remains between the crests and roots of the threads because of the taper). This means that NPT fittings should be [[burr (edge)|burr]]-free and lubricated using a [[lubricant]] like lubricating paste or thread seal tape. The use of tape also helps to limit corrosion on the threads, which otherwise can make future disassembly nearly impossible.

Commonly used sizes are {{frac|1|8}}, {{1/4}}, {{frac|3|8}}, {{1/2}}, {{3/4}}, 1, {{frac|1|1|4}}, {{frac|1|1|2}}, 2, {{frac|2|1|2}}, 3, {{frac|3|1|2}}, 4, 5, and 6&nbsp;inch, as [[Pipe (material)|pipe]] and fittings by most US suppliers. Sizes smaller than {{frac|1|8}}&nbsp;inch are occasionally used for compressed air, while sizes larger than 6&nbsp;inches are often joined by other methods.

==Specifications==
NPT is defined by [[ANSI]]/[[American Society of Mechanical Engineers|ASME]] standard B1.20.1<!-- covers threads of 60-degree form with flat crests and roots in sizes from 1/16 inch to 24-inch Nominal Pipe Size (NPS) -->.<ref name="B1.20.1">{{Cite web |url=http://www.hemcogages.com/ansi.htm |title=ANSI Thread Series Designations |access-date=2008-04-27 |archive-url=https://web.archive.org/web/20080514135011/http://www.hemcogages.com/ansi.htm |archive-date=2008-05-14 |url-status=dead }}</ref>

The taper rate for all NPT threads is 1 inch of diameter in 16 inches of length ({{convert|3/4|in/ft|1|disp=or|sp=us}}) measured by the change of diameter (of the pipe thread) over distance of thread. The half-angle (between the taper surface and the axis of the pipe) is [[inverse tangent|arctan]]({{frac|1|32}}) ≈ 1.7899° ≈ 1°&nbsp;47′.

The standard for [[Nominal Pipe Size]] (often abbreviated NPS, which should not be confused with the abbreviation NPS for the straight thread form standard) is loosely related to the inside diameter of [[Schedule 40]] series of sizes. Because of the pipe wall thickness of Schedule pipe, the actual diameter of the NPT threads is larger than the Nominal Pipe Size diameter, and considerably so for small sizes. Pipe of a given size in a different Schedule than Schedule 40 provides a different wall thickness while maintaining the same outside diameter and thread profile as Schedule 40. Thus the inside diameter of a given size of Schedule pipe differs from the Nominal Pipe Size, while outside diameters for a given nominal Schedule size are the same between Schedules.

=== Thread form ===
National Pipe Thread series have the same 60° included angle as [[Screw thread#History of standardization|Sellers thread]]. On the other hand, for sealing capability, tapered (pressure-tight) threads have crest and root shapes that differ from Sellers. For example, the NPT has a crest width of 0.038 to 0.062 pitch, which is sharper than the 0.125 pitch of Sellers.
<ref name="B1.20.1"/>

=== National pipe taper fuel (NPTF) ===
'''National Pipe Taper Fuel''' ('''NPTF''', also called '''Dryseal American National Standard Taper Pipe Thread''', defined by ASME B1.20.3) is designed to provide a more leak-free seal without the use of [[polytetrafluoroethylene|PTFE]] tape (often referred to by the popular brand name "Teflon") or another sealant compound. NPTF threads have the same basic shape but with crest and root heights adjusted for an interference fit, eliminating the spiral leakage path.

== Standard sizes ==
{| class="wikitable"  style="text-align:center"
|+ American Society of Mechanical Engineers National Pipe Thread Taper (NPT)<ref>[http://www.engineeringtoolbox.com/npt-national-pipe-taper-threads-d_750.html Engineering toolbox]</ref>
|-
!           rowspan="2" | [[Nominal size|Nominal]] <br />pipe size
!           rowspan="2" | [[Screw thread#Lead, pitch, and starts|Thread <br />density]]
! colspan=2 rowspan="2" | [[Lead (engineering)|Thread pitch P]]
! colspan=3             | Hand-tight engagement<ref name="piping-designer">{{Cite web|url=http://www.piping-designer.com/index.php/disciplines/mechanical/84-stationary-equipment/fastener/1156-national-pipe-thread?title=National_Pipe_Thread|title = National Pipe Thread}}</ref>
! colspan=3             | Effective thread<ref name="piping-designer" />
!           rowspan="2" | Overall <br />length L<sub>4</sub><ref name="piping-designer" />
! colspan=2 rowspan="2" | [[Real versus nominal value#Engineering|Actual]] outside <br />diameter D
! colspan=2 rowspan="2" | [[List of drill and tap sizes|Tap drill]]
|-
! Length L<sub>1</sub>
! Turns
! Diameter E<sub>1</sub>
! Length L<sub>2</sub>
! Turns
! Diameter E<sub>2</sub>
|-
! inch
! inch{{sup|−1}}
! inch !! mm
! inch
! 
! inch
! inch
! 
! inch
! inch
! inch !! mm
! inch !! mm
|-
| {{frac|1|16}}
| 27
| {{convert|0.03703704|in|mm|4|disp=table}}
| 0.1600 || 4.32 || 0.28118
| 0.2611 || 7.05 || 0.2875

| 0.3896
| {{convert|0.313|in|mm|3|disp=table}}
| ||
|-
| {{frac|1|8}} || 27
| {{convert|0.03703704|in|mm|4|disp=table}}
| 0.1615 || 4.36 || 0.37360
| 0.2639 || 7.13 || 0.38000
| 0.3924
| {{convert|0.405|in|mm|3|disp=table}}
| {{convert|0.339|in|mm|4|disp=table}}
|-
| {{frac|1|4}}
| 18
| {{convert|0.05555555|in|mm|4|disp=table}}
| 0.2278 || 4.10 || 0.49163
| 0.4018 || 7.23 || 0.50250
| 0.5946
| {{convert|0.540|in|mm|3|disp=table}}
| {{convert|7/16|in|mm|3|disp=table}}
|-
| {{frac|3|8}}
| 18
| {{convert|0.05555555|in|mm|4|disp=table}}
| 0.2400 || 4.32 || 0.62701
| 0.4078 || 7.34 || 0.63750
| 0.6006
| {{convert|0.675|in|mm|3|disp=table}}
| {{convert|37/64|in|mm|3|disp=table}}
|-
| {{frac|1|2}}
| 14
| {{convert|0.07142857|in|mm|4|disp=table}}
| 0.3200 || 4.48 || 0.77843
| 0.5337 || 7.47 || 0.79178
| 0.7815
| {{convert|0.840|in|mm|4|disp=table}}
| {{convert|23/32|in|mm|4|disp=table}}
|-
| {{frac|3|4}}
| 14
| {{convert|0.07142857|in|mm|4|disp=table}}
| 0.3390 || 4.75 || 0.98887
| 0.5457 || 7.64 || 1.00178
| 0.7935
| {{convert|1.050|in|mm|4|disp=table}}
| {{convert|59/64|in|mm|4|disp=table}}
|-
| 1
| {{frac|11|1|2}}
| {{convert|0.08695652|in|mm|4|disp=table}}
| 0.4000 || 4.60 || 1.23863
| 0.6828 || 7.85 || 1.25631
| 0.9845
| {{convert|1.315|in|mm|4|disp=table}}
| {{convert|1+5/32|in|mm|4|disp=table}}
|-
| {{frac|1|1|4}}
| {{frac|11|1|2}}
| {{convert|0.08695652|in|mm|4|disp=table}}
| 0.4200 || 4.83 || 1.58338
| 0.7068 || 8.13 || 1.60131
| 1.0085
| {{convert|1.660|in|mm|4|disp=table}}
| {{convert|1+1/2|in|mm|4|disp=table}}
|-
| {{frac|1|1|2}}
| {{frac|11|1|2}}
| {{convert|0.08695652|in|mm|4|disp=table}}
| 0.4200 || 4.83 || 1.82234
| 0.7235 || 8.32 || 1.84131
| 1.0252
| {{convert|1.900|in|mm|4|disp=table}}
| {{convert|1+47/64|in|mm|4|disp=table}}
|-
| 2
| {{frac|11|1|2}}
| {{convert|0.08695652|in|mm|4|disp=table}}
| 0.4360 || 5.01 || 2.29627
| 0.7565 || 8.70 || 2.31630
| 1.0582
| {{convert|2.375|in|mm|4|disp=table}}
| {{convert|2+7/32|in|mm|4|disp=table}}
|-
| {{frac|2|1|2}}
| 8
| {{convert|0.12500000|in|mm|4|disp=table}}
| 0.6820 || 5.46 || 2.76216
| 1.1375 || 9.10 || 2.79063
| 1.5712
| {{convert|2.875|in|mm|4|disp=table}}
| {{convert|2+5/8|in|mm|4|disp=table}}
|-
| 3
| 8
| {{convert|0.12500000|in|mm|4|disp=table}}
| 0.7660 || 6.13 || 3.38850
| 1.2000 || 9.60 || 3.41563
| 1.6337
| {{convert|3.500|in|mm|4|disp=table}}
| {{convert|3+1/4|in|mm|4|disp=table}}
|-
| {{frac|3|1|2}}
| 8
| {{convert|0.12500000|in|mm|4|disp=table}}
| 0.8210 || 6.57 || 3.88881
| 1.2500 || 10.00 || 3.91563
| 1.6837
| {{convert|4.000|in|mm|4|disp=table}}
| {{convert|3+3/4|in|mm|4|disp=table}}
|-
| 4
| 8
| {{convert|0.12500000|in|mm|4|disp=table}}
| 0.8440 || 6.75 || 4.38713
| 1.3000 || 10.40 || 4.41563
| 1.7337
| {{convert|4.500|in|mm|4|disp=table}}
| {{convert|4+1/4|in|mm|4|disp=table}}
|-
| {{frac|4|1|2}}
| 8
| {{convert|0.12500000|in|mm|4|disp=table}}
| || || 
| || || 
| 
| {{convert|5.000|in|mm|4|disp=table}}
| {{convert|4+3/4|in|mm|4|disp=table}}
|-
| 5
| 8
| {{convert|0.12500000|in|mm|4|disp=table}}
| 0.9370 || 7.50 || 5.44929
| 1.4063 || 11.25 || 5.47863
| 1.8400
| {{convert|5.563|in|mm|4|disp=table}}
| {{convert|5+9/32|in|mm|4|disp=table}}
|-
| 6
| 8
| {{convert|0.12500000|in|mm|4|disp=table}}
| 0.9580 || 7.66 || 6.50597
| 1.5125 || 12.10 || 6.54063
| 1.9462
| {{convert|6.625|in|mm|4|disp=table}}
| {{convert|6+11/32|in|mm|4|disp=table}}
|-
| 8
| 8
| {{convert|0.12500000|in|mm|4|disp=table}}
| 1.0630 || 8.50 || 8.50003
| 1.7125 || 13.70 || 8.54063
| 2.1462
| {{convert|8.625|in|mm|4|disp=table}}
| ||
|-
| 10
| 8
| {{convert|0.12500000|in|mm|4|disp=table}}
| 1.2100 || 9.68 || 10.62094
| 1.9250 || 15.40 || 10.66563
| 2.3587
| {{convert|10.750|in|mm|4|disp=table}}
| ||
|-
| 12
| 8
| {{convert|0.12500000|in|mm|4|disp=table}}
| 1.3600 || 10.88 || 12.61781
| 2.1250 || 17.00 || 12.66563
| 2.5587
| {{convert|12.750|in|mm|4|disp=table}}
| ||
|-
| 14
| 8
| {{convert|0.12500000|in|mm|4|disp=table}}
| 1.5620 || 12.50 || 13.87263
| 2.2500 || 18.00 || 13.91563
| 2.6837
| {{convert|14.000|in|mm|4|disp=table}}
| ||
|-
| 16
| 8
| {{convert|0.12500000|in|mm|4|disp=table}}
| 1.8120 || 14.50 || 15.87575
| 2.4500 || 19.60 || 15.91563
| 2.8837
| {{convert|16.000|in|mm|4|disp=table}}
| ||
|-
| 18
| 8
| {{convert|0.12500000|in|mm|4|disp=table}}
| 2.0000 || 16.00 || 17.87500
| 2.6500 || 21.20 || 17.91563
| 3.0837
| {{convert|18.000|in|mm|4|disp=table}}
| ||
|-
| 20
| 8
| {{convert|0.12500000|in|mm|4|disp=table}}
| 2.1250 || 17.00 || 19.87031
| 2.8500 || 22.80 || 19.91563
| 3.2837
| {{convert|20.000|in|mm|4|disp=table}}
| ||
|-
| 24
| 8
| {{convert|0.12500000|in|mm|4|disp=table}}
| 2.3750 || 19.00 || 23.86094
| 3.2500 || 26.00 || 23.91563
| 3.6837
| {{convert|24.000|in|mm|4|disp=table}}
| ||
|}
[[File:NPT_Dimensions.svg|frame|center|alt=A NPT dimensions|Hand-tight and effective thread engagement lengths]]

==History==
{{see also|Screw thread#History of standardization}}
In 1864, [[William Sellers]], then president of [[Franklin Institute]], presented a standard for nuts, bolts, and screws. Out of this effort came the first [[United States Standard thread]]s, including pipe threads.<ref>{{Cite web |url=https://www.engineerily.com/1304161-bsp-and-npt-threads-detailed-explanation-differences.htm |title=BSP and NPT threads - Detailed Explanation, Differences |access-date=2016-04-17 |archive-url=https://web.archive.org/web/20160426084836/https://www.engineerily.com/1304161-bsp-and-npt-threads-detailed-explanation-differences.htm |archive-date=2016-04-26 |url-status=dead }}</ref>

==See also==
{{Div col}}
* [[AN thread]]
* [[British Standard Pipe]]
* [[Fire hose thread]]
* [[Garden hose thread]]
* [[Gender of connectors and fasteners]]
* [[Panzergewinde]]
* [[Thread angle]]
* [[Threaded pipe]]
{{div col end}}

==References==
{{Reflist}}

==Bibliography==
* {{MachinerysHandbook25e}}

==External links==
* [http://www.amesweb.info/Screws/NPT_National_Taper_Pipe_Threads.aspx NPT Pipe Thread Dimensions]
* [https://web.archive.org/web/20120721055029/http://www.asme.org/products/codes---standards/pipe-threads--general-purpose--inch ASME B1.20.-1983 Pipe Threads, General Purpose, Inch ]
* [https://www.threadspecification.com/npt/ NPT Taper Pipe Threads]

{{DEFAULTSORT:National Pipe Thread}}
[[Category:Thread standards]]
[[Category:Piping]]
[[Category:Plumbing]]
[[Category:Standards of the United States]]

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