NPT Drill Pipe

National Pipe Thread Taper(NPT) is a U.S. standard for tapered threads used on threaded pipes and fittings, in contrast to straight threads that are found on a bolt, a taper thread will pull tight and therefore make a fluid-tight seal. Commonly used sizes are 1/8, 1/4, 3/8, 1/2, 3/4, 1, 1 1/4, 1...

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National Pipe Thread Taper(NPT) is a U.S. standard for tapered threads used on threaded pipes and fittings, in contrast to straight threads that are found on a bolt, a taper thread will pull tight and therefore make a fluid-tight seal.

National Pipe Thread Taper
NPT drill pipe


Commonly used sizes are 1/8, 1/4, 3/8, 1/2, 3/4, 1, 1 1/4, 1 1/2, and 2inch, appearing on pipes and fittings by most U.S. suppliers. Size smaller than 1/8inch are occasionally used for compressed air, while sizes larger than 2inches are uncommon, due to the use of alternative methods of joining that are used with these larger sizes.


The following is Standard pipe thread recommended tap size and drilled pilot hole for taper.


National Standard Taper Pipe threads size NPT Chart

TAPER PIPES SIZES-NPT

STRAIGHT PIPES SIZES-NPS

TAP SIZE

DRILL SIZE

TAP SIZE

DRILL SIZE

1/8-27

R

1/8-27

S

1/4-18

7/16

1/4-18

29/64

3/8-18

37/64

3/8-18

19/32

1/2-14

23/32

1/2-14

47/64

3/4-14

59/64

3/4-14

15/16

1"-11-1/2

1-5/32

1"-11-1/2

1-3/4

1-1/4-11-1/2

1-1/2

1-1/4-11-1/2

1-33/64

1-1/2-11-1/2

1-47/64

1-1/2-11-1/2

1-3/4

2"-11-1/2

2-7/32

2"-11-1/2

2-7/32

2-1/2-8

2-5/8

2-1/2-8

2-21/32

3"-8

3-1/4

3"-8

3-9/32

3-1/2-8

3-3/4

3-1/2-8

3-25/32

4"-8

4-1/4

4"-8

4-9/32


Some part of NPT Drilling pipe parameters:

Material

Pin Dimensions

Box Dimensions

Thread

 

Tool Joint Name & Nominal Size

O.D.

Make to Dia.

Pin Length

Pin ID

Pin Dia. @ Base

Box Length

Box Max ID

Taper

Thread / Inch

Thread Form

1″ NPT

1 3/4″

 

1″

1″

1.325″

1 1/4″

1 1/8″

3/4″

11 1/2

TAPER

1″ NPT LH

1 3/4″

 

1″

1″

1.325″

1 1/4″

1 1/8″

3/4″

11 1/2

TAPER

1 1/4″ NPT

2″

 

1″

1 1/4″

1.660″

1 1/4″

1 3/8″

3/4″

11 1/2

TAPER

1 1/2″ NPT

2 1/4″

 

1 1/8″

1 1/2″

1.950″

1 3/8″

1 5/8″

3/4″

11 1/2

TAPER

2″ NPT

2 3/4″

 

1 1/8″

2″

2.385″

1 5/8″

2 1/8″

3/4″

11 1/2

TAPER

2″ NPT LH

2 3/4″

 

1 1/8″

2″

2.385

1 5/8″

2 1/8″

3/4″

11 1/2

TAPER

2 1/2″ NPT

3 1/4″

 

1 9/16″

2 1/2″

2.875″

1 3/4″

2 5/8″

3/4″

8

TAPER

3″ NPT

4″

 

1 5/8″

3″

3.500″

1 7/8″

3 1/8″

3/4″

8

TAPER

3″ NPT LH

4″

 

1 5/8″

3″

3.500″

1 7/8″

3 1/8″

3/4″

8

TAPER

3 1/2″ NPT

4 5/8″

 

1 11/16″

3 1/2″

4.000″

2 1/16″

3 5/8″

3/4″

8

TAPER

3 1/2″ NPT LH

4 5/8″

 

1 11/16″

3 1/2″

4.000″

2 1/16″

3 5/8″

3/4″

8

TAPER

4″ NPT

5 1/4″

 

1 3/4″

4″

4.510″

2 1/4″

4 1/8″

3/4″

8

TAPER

4″ NPT LH

5 1/4″

 

1 3/4″

4″

4.510″

2 1/4″

4 1/8″

3/4″

8

TAPER

4 1/4″ NPT

 

 

 

4 1/4″

4.250″

 

 

3/4″

8

TAPER

5″ NPT

6 5/16″

 

2″

5″

5.563″

2 1/2″

5 1/4″

3/4″

8

TAPER

6″ NPT

7 3/8″

 

2″

6″

6.625″

2 1/2″

6 1/4″

3/4″

8

TAPER


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 PTFE, 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 fittings in which the threads merely hold the pieces together and do not provide the seal, as the thread body is tapered(0.75 in/ft or 62.5mm/m) a larger diameter keeps compressing into a smaller diameter and finally forms a seal(no means that NPT fittings should be burr-free and lubricated using a lubricating material like lubricating paste or tape, the use of tape also helps to limit corrosion on the threads, which otherwise can make future disassembly nearly impossible.


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