|
National Standard Pipe Taper Threads
|
Male
threads:
Measure the outside diameter of the large portion of the
thread at "A"; Find figure nearest this dimension in
column 1 or 2 of chart. The dimension in column 3 will
be your nominal pipe thread size. |
|
Female Threads:
Measure top diameter of
thread at "B"; Find figure nearest this dimension in
column 1 or 2 of chart. The dimension in column 3 will
be your nominal pipe thread size. |
|
Column 1 |
Column 2 |
Column 3 |
Column 4 |
Column 5 |
|
OD Fraction Inch
(for quick
reference only) |
Actual (decimal) Inch. |
Pipe
Thread Size |
Normal engagement for tight
joint (dimension "C") |
Threads per Inch |
|
5/16 |
0.3125 |
1/16 |
0.2611 |
27 |
|
13/32 |
0.405 |
1/8 |
0.2639 |
27 |
|
35/64 |
0.540 |
1/4 |
0.4018 |
18 |
|
43/64 |
0.675 |
3/8 |
0.4078 |
18 |
|
27/32 |
0.840 |
1/2 |
0.5337 |
14 |
|
1-3/64 |
1.050 |
3/4 |
0.5457 |
14 |
|
1-5/16 |
1.315 |
1 |
0.6828 |
11-1/2 |
|
1-21/32 |
1.660 |
1-1/4 |
0.7068 |
11-1/2 |
|
1-29/32 |
1.900 |
1-1/2 |
0.7235 |
11-1/2 |
|
2-3/8 |
2.375 |
2 |
0.7565 |
11-1/2 |
|
2-7/8 |
2.875 |
2-1/2 |
1.1375 |
8 |
|
3-1/2 |
3.5 |
3 |
1.2000 |
8 |
|
4 |
4.0 |
3-1/2 |
1.2500 |
8 |
|
4-1/2 |
4.5 |
4 |
1.3000 |
8 |
|
Two common pipe
thread sizes exist, the tapered National Pipe Thread
(NPT) and the straight National Standard Free-Fitting
Straight Mechanical Pipe Thread (NPSM). The tapered
threads are for joining and sealing, the straight
threads are only for joining. The Dry-seal thread (NPTF)
allows for joining without sealants. Three less common
threads exist, the Garden Hose Thread (GHT), Fire Hose
Coupling (NST) and British Standard Taper Pipe Thread (BSPT).
The NPT and NPTF threads are interchangeable with
sealants such as PTFE tape. None of the other thread
standards are interchangeable. Female NPT threads can be
designated as "FPT" and male NPT threads can be
designated as "MPT."
Pipe sizes do not refer to any physical dimensions. The
outside diameter of each pipe or fitting must be
measured and compared to the table for size
identification. For example, a 3/4" NPT pipe thread has
an outside diameter of 1.050 inches. Each thread size
has a defined number of threads per inch (TPI). The 3/4"
NPT pipe thread has 14 threads per inch. Both the TPI
and OD of the thread are required for positive
identification of thread size because several sizes have
the same TPI.
|
| Definition
of pipe thread acronyms |
| NPT |
National Pipe Thread |
| FPT |
Female Pipe Thread |
| MPT |
Male Pipe Thread |
| PTF |
SAE short tape pipe thread |
| NPTF |
American National taper pipe thread for dryseal
pressure-tight joints |
| NPSM |
American National straight pipe thread for
mechanical joints |
| NPSI |
American National straight intermediate pipe thread |
| |
For NPT threads a sealant compound or Teflon tape must
be used for a leak-free seal. For NPTF no sealant is needed for a sealing.
Characteristics of NPT (also known as ANSI/ASME B1.20.1
Pipe Threads, General Purpose):
- tapered thread 1o
47'
- truncation of roots and crests are flat
- 60o thread
angle
- pitch is measured in threads per inch
Note! Pipe sizes
do not refer to any physical dimensions. The outside diameter of a pipe or
fitting must be measured and compared to a table for size identification. A
3/4" NPT pipe thread has an outside diameter - OD - of 1.050
inches.
Each thread size has a defined number of threads per
inch - TPI, or pitch. The 3/4" NPT pipe thread has 14 threads
per inch. Both the TPI and OD of the thread are required for positive
identification of thread size because more than one size have the same TPI.
| NPT - American
Standard Pipe Thread Taper 1) |
Pipe Size
(inches) |
Threads per Inch
TPI - pitch |
Nominal Pipe
OD
(inches) |
Tap Drill
(inches) |
| 1/16" |
27 |
0.313 |
|
| 1/8" |
27 |
0.405 |
R |
| 1/4" |
18 |
0.540 |
7/16 |
| 3/8" |
18 |
0.675 |
37/64 |
| 1/2" |
14 |
0.840 |
23/32 |
| 3/4" |
14 |
1.050 |
59/64 |
| 1" |
11-1/2 |
1.315 |
1-5/32 |
| 1-1/4" |
11-1/2 |
1.660 |
1-1/2 |
| 1-1/2" |
11-1/2 |
1.900 |
1-47/64 |
| 2" |
11-1/2 |
2.375 |
2-7/32 |
| 2-1/2" |
8 |
2.875 |
2-5/8 |
| 3" |
8 |
3.500 |
3-1/4 |
| 3-1/2" |
8 |
4.000 |
3-3/4 |
| 4" |
8 |
4.500 |
4-1/4 |
| 4 1/2" |
8 |
5.000 |
4-3/4 |
| 5" |
8 |
5.563 |
5-9/32 |
| 6" |
8 |
6.625 |
6-11/32 |
| 8" |
8 |
8.625 |
|
| 10" |
8 |
10.750 |
|
| 12" |
8 |
12.750 |
|
| 14" |
8 |
14.000 |
|
| 16" |
8 |
16.000 |
|
1) The taper is 1/16
inch in an inch, which is the same as 3/4 inch in a foot (angle 1o
47')
NPT threads are not interchangeable with NPS - National
Pipe Straight - threads.
NPT threads may look similar to
ISO 7/1
threads. However, ISO and NPT threads should not be mixed. ISO threads
have 55o taper angle versus 60o for NPT. The NPT root
and crest configurations are also different from ISO. For ISO threads pitch
is usually measured in millimeters (may be expressed in Inch). The pitch are
different. |
